Everyone else has already given good advice with regard to paint, brushes, and YouTube tutorials, so I'll just add this:

In your local children's toy store, buy a cheap bag of those little army men on which to practice your painting skills. You can get a bag of several dozen figures for very little money, so you can mess up (and you will when you're just learning) without feeling too bad about wasting money.

Not much more tips I can give other than what as already been said, so I,ll just give you my personnal one that I consider most important:

-Thin your paint with a little water. You'll probably need to do more than one coat this way, but you won't hide the details and fill the recess with a paint too thick. The brand I mostly use is Reaper's Miniatures. It doesn't need as much thinning as the paint you'll find in your general craft store and have lot of pigments, so even if you thin a lot, it will keep a good texture. The bottle also have a eyedropper so you have more control on your quantity when mixing.

-After basecoating (although I heard that you don't have to with X-Wing miniatures, I still have to do a repaint) What I do first is apply evenly the primary color(2 to 4 coat depending on color). Then I do the shadow with a darker color by thinning the paint with water (1 part paint to 5-8part water, depending on the paint consistency) and apply it on the base color. Instead of thinning your paint, you can buy ink made for this purpose. What the thinned water or ink will do is go into all the recess of the model and make the details pop even more. With a thinned down paint, repeat for 2 to 4 coat, darkening your paint everytime. After that, you do the highlights with a thicker paint starting with the basic color and going for a lighter paint evertime and covering smaller and smaller area. This add volume to your miniature.

-Practice a lot and be proud of your accomplishment. Learning to paint is not easy and take time and patience. Don't expect to propaint after just a few miniatures (unless you're especially good in art). But you'll see that just by doing the basic (base color/shadow/highlights) you can achieve very satisfying results.

-Concerning the brush, I use a size 0 liner and it work fine. Don't overdo it with a 10/0 size, those are too small and unecessary, you can do a dot as small without going for the smallest brush.

-And a good rule of thumb: If you can't reach it, you probably won't see it. There is some parts on a preassembled miniature that is very hard to reach with your brush. Before forcing yourself and risking to mess the rest of the miniature, be sure that it is indeed a part that you will see once finished on the table.

Also.. something I haven't seen.. unless I missed it.. get a good sealer.. either a varnish as some call it or .. I use dullcote, or gloss cotes when I need them. You want to always spray a miniature after the paints have all dried. Give it a night to rest, and then seal it the next day, it will help keep the paint job from wearing off from moving it around.

I use testors gloss cotes and Armory dullcote. I've had good experiences with those. Though they can be pricy.. they do wonders for preservation of your work

You will need to learn how to dry brush. A cheap brush from Wal-mart can do that.

You will need to do some tiny detail. That requires a very fancy brush that keeps a good point. I recommend the Winsor-Newton Series 7 brushes. While some say they are the best brush ever, I disagree, but they are perfect for this job.

For a sealant, you can just use any matte spray. Just make sure it's not a humid day and you follow the instructions for distances. Doing several light coats is better than one heavy.

A tip when spraying.

Hold the can 8 to 10 inches from the piece and start the spray before you are on the mini, and stop after you are of the mini. Use a straight even motion. This will give a great coverage of the model, and an even coat.