1) How to get started:
Know your ending. Make sure you're clear on where you're going before you start. You'll need a clear idea of what you want to write, of course. Make notes, plan out a basic plot, maybe even make a timeline so that you know what order things are going to happen in. I find I have to make plenty of notes, and let things find their place in the story. I give it time to stew, and when it's ready to be told, I get impatient to write it. Make sure you have long periods of peace and quiet in which to write, so you can relax into it, and try and gradually lengthen the amount of time you can spend writing as you get into it. But the most important thing is to know your ending; you can always change it if you want, but it gives you something to aim at.
2) What makes a good opening:
The most important requirement for an opening passage is to emotionally involve your reader as quickly as possible. If you are writing a thriller, start with a piece of action. If it's a drama, start with a character facing a problem (preferably one of your main characters) or something that establishes your character's personality and makes the reader warm to them. Another good starting point is to pose a question, or create a mystery - make the reader ask what is happening, and make them want to read on. Avoid starting any story with long descriptive passages of landscapes, or weather, or the world around your characters; you can't get emotionally involved with buildings or hills. I can sometimes jump between two or more narratives at the beginning of the book, but it's best to keep to one if you can, so the reader can follow it and get engrossed quicker and easier. Whatever you do, remember you only have a few pages to grab your reader's attention. The start of your story is the single most difficult and important part.
Any plot-driven story is a mixture of creativity and logic. If you're driven to write, you'll find that some scenes just come to you out of the blue, and some will have to be worked up. Connecting them can then be an exercise in problem-solving. Although I do plan out my stories, I'm not as deliberate in my plotting techniques as some other writers. You'll hear about those who write pieces of plot out on cards and lay them to be rearranged on a table or floor, or some people form 'trees' of events, and timelines to help make connections. Other writers don't plan at all, preferring to write in a more spontaneous way and iron out any kinks in subsequent drafts. I just make copious notes, and the good bits stick in my mind. Once I've written something down, I'll tend to remember it without checking back to the note, and as I work the story over in my mind, bits fall into place. For sequencing though, you may need to plot out a timeline to keep track of what event happened on what day, etc.
There are no hard and fast rules for coming up with a good plot. A gripping start is vital, to get the reader involved. The middle of the story, where you are most likely to get bogged down, has to have sufficient pace to keep your hold over the reader, but if you're writing a thriller, you'll need to cool the pace down a bit here and there to take a breather. Action has to be contrasted with contemplative pieces for maximum effect. If it's a drama, or romance, the problem that has hooked the reader has to be maintained throughout, or even replaced with a worse one as you go along. Even in a plot-driven story, believable characters are crucial, and you will have to get away from the direct line of your plot sometimes to let them strut their stuff a little. This will also stop your plot from becoming too linear, which can make it predictable -- any run-of-the-mill Hollywood film will demonstrate both the mechanics of writing a plot, and the problems of sticking too close to a formula.
As I said, there are no winning rules for coming up with a plot; but there are plenty of guidelines. Learn them, use them, and then figure out when to ignore them. You can't be original unless you strike out on your own.
Somebody could write an encyclopedia on how to come up with characters, and not cover a fraction of the subject. The best way to start creating characters is to use personality traits of people you know, or work with. There are an infinite number of quirks and mannerisms that you can add to a character, but understanding how they tick is the first thing you need to know. What they love, why they do the things they do, what they're scared of, etc. Study the people around you, learn to enjoy the differences between people, and savour the little things that they do that make them who they are.
Characters are a vital element of any story, as they are what your reader is going to relate to. Think of somebody you like for a hero, and the characteristics of someone you don't like for a villain, and then mix and match for effect. Don't be afraid to steal characters from books, television and films, and twist them to make them fit in your story - everybody starts learning a skill by copying. Just make sure you're nicking good ones, and hide your theft well! One of the most appealing aspect of any character is their flaws. Notice how many thrillers try to give their two-dimensional, hard-bitten heroes character by making him an ex-drug addict, or an alcoholic, or killing off their partner so they can be bitter and twisted. Try and be a bit more original, but the basic idea works. It's hard to love someone who's perfect, we relate to people who have the same flaws as ourselves.
You'll know when a character is working because they'll take on a life of their own, when their character starts dictating where your plot can go: they would do this, but they wouldn't do that, then you've created a personality that will lift off the page.
The setting for any story is important, but it must never get in the way of the plot or the characters. That said, you have to make it believable in order to create a world in which your characters live. Settings are often where a writer can fall down because they don't know enough about a certain type of environment, and aren't interested enough, or are too lazy to research it.
If you're going to describe something, learn the terms. Trees and bushes have names, buildings have styles of architecture, décor has features. Don't get too caught up in the detail, but a certain familiarity is necessary to describe anything. If you're describing a building, base it on one you know; the same with a forest, or a city street. Think in terms of colour, texture, lighting and space. Imagine writing a screenplay, where your descriptions have to be made into a film. If you have trouble imagining these kinds of things, look at pictures in newspapers, magazines, and even films. Imagine trying to describe them to a friend - or even try it for real.
If you want to create a fantasy world, use things you know as your building blocks. Strike the balance between the familiar and the weird. If it's too far out, you could lose your reader, or spend so much time on description that the story suffers. Keep the truly weird for short, sharp bursts. To create something new, it is often useful to look at something that exists and give it a twist; for instance, imagine a field of grass where the grass is metal, or an apple with a worm city inside. Using familiar terms gives the reader some footholds to hang onto.
The setting is the world around your characters, and has to be believable, or else they're just going to be actors on an unconvincing stage, hoping your reader has the imagination to do your work for you.
There's not a whole lot to say about dialogue. Listen to the way people talk, make notes of funny or striking phrases. The simple rule with dialogue is that if you can't say it out loud without sounding awkward, don't use it. If you need to, find some time alone, and read what you've written out loud. Say it as the character would say it in that situation, as an actor would. Hardly anybody speaks with perfect grammar or says exactly what they mean to say - nobody speaks without adding the odd 'eh,' or 'em,' or 'y'know'. Perfect diction is for robots, have the characters make mistakes in their speech. Dialogue can make or break your characters. Listen to how people speak and reproduce it.
7) A good ending:
The end of the story must climax. The risk to the characters must be at its greatest, and they must look as if they are on the brink of losing what is most important to them. Whether they do or not is up to whether you're a fan of happy endings. Most readers are. Quite often, I find a bitter-sweet ending is best; the characters can win out, but not without a cost to them. The best endings should leave the characters changed in some way. Don't climax too early, and don't drag an ending out for too long. You want to leave the reader on a high, not bore them right at the end of the story after all your hard work getting them there.
8) Any other advice?
You could spend the rest of your life reading what others write on HOW to write. Nobody has the definitive answers - I certaily don't. Don't get too caught up in this. The time you spend reading these things could be spent writing, and that's what you should be doing. Writers write, so get on with it!
If you're getting more serious about your writing, and are thinking of trying to get published, I suggest you check out cb info on the Children's Books Ireland website. Or you can get youserlf a copy of the The Artists' and Writers' Yearbook or The Children's Writers' and Artists' Yearbook.