First, make sure you're using decent vinyl. I've used Oracal and 3M 1080 before and they're easy to work with (relatively).
Second, check to see what heating method the manufacturer recommends. Some specify a torch, some a heat gun.
Get some knifeless tape. Basically it's a bit of really thin string that gets taped down to the surface. You put the vinyl over it and then pull it up to cut. That's the only way you're going to get seams that look halfway decent.
Get tack cloths, alcohol, and rags that don't shed.
You'll need a good squeegee. Or even a bad one. The little felt-covered one that a lot of the eBay sellers include in their "kits" will get the job done until the felt wears away.
Space. You need to be able to move and work around what you're covering.
3M makes a primer called "Primer 94". You want that.
Start with large, flat surfaces to get some experience with the material and to build up your confidence. Ideally, you will have as few seams as is humanly possible because even with knifeless tape, any seam is going to be pretty visible. That means you want to plan your seams around body lines or color changes.
For your long, flatish spot, cut your vinyl so that it's too big by a decent amount. It's way better to scrap a couple extra inches a vinyl rather than the whole piece because it was just that much too small. Once you've got the paint clean, you'll want to wipe it down with the tack cloth and alcohol to make sure there's nothing on the surface. Pretty much anything you try to cover over will show up, so the cleaner you can get it, the better. Be sure to clean not only the top of the surface, but the edges and the underside around the edges as well. Apply the Primer 94 to the edges and to the underside of the edges. It doesn't need to be on the whole surface - as long as we can keep the vinyl from coming up, it'll stay in place. I don't remember what the instructions for the 94 are, but follow them.
It works best with two people, especially for larger areas like a hood. You don't need to remove all of the backing. Take a section out of the backing out of what will be the center and lay it down. Check to make sure that it's where it needs to be and that it's going to reach to the edges and have plenty of overhang. At this point, you won't hurt anything by moving it. You can pop a small amount of heat on to the adhered section to release it if you need to, but if you haven't squeegeed it yet, it should release on its own. Once you're happy with it, you can start pulling more of the backing off and start laying the vinyl to the surface. Don't take big bites, just work in small bits, squeegeeing out from the center to prevent bubbles from forming. You're going to be pulling on the edge of the vinyl while pushing the center-most portion down and squeegeeing towards yourself.
If you get a bubble or a wrinkle, you can just peel the vinyl back and work it out. Sometimes giving it a little heat can help. If you stick the adhesive side to itself, that gets a little more difficult, but you can still carefully peel them apart. Put a little heat on it and you'll smooth the vinyl back out. Basically you want to resolve any bubbles as soon as possible. It's pretty easy to lift the vinyl off and readjust when the bubble is an inch or two in. If you have to pull the whole thing, you're screwed.
Just keep working in very small steps until you get to the edge. I don't like to start on the corner, but I'll start in the middle of an edge and give the vinyl a little bit a heat so I can stretch it over and around the edge and squeegee it to the underside. You're going to want about a centimeter or so of overlap underneath and you don't want any gaps, it needs to conform exactly to the surface in order to make sure it doesn't pop off later on. Some heat will make it much more compliant and it will want to just relax itself into the groove, as it were.
Work along the edge until you get to the first corner. You're going to need to stretch the vinyl a bit with some heat to get it to go around the edge, and then cut a slit in the underside portion to get it to stick properly. Careful about how much cut you put in there - you don't want the cut to be visible on the edge. If you're bunching up, pull the vinyl back a little, put some heat in, and stretch it so that the wrinkling comes out. It might take a few attempts, but you'll be able to get that out eventually. Once you have it adhered, go ahead and trim the underside so you've got about a centimeter or so attached. Don't trim it until you're confident that it's in place, because trying to pull on vinyl when you only have a tiny bit to grasp is a good way to tear it, especially when it's hot.
Doing those corners on a flat section will get you psyched up to do some curves. The folks that do this a lot apparently practice by wrapping bowling pins in a single sheet of vinyl. If you want a really really really good job, then you're going to need to buy some bowling pins and start practicing a lot. I'm not that patient, so I went with a good enough approach. Let's take the trunk of a Neon, for example:
First of all, notice that you can see the holes from the spoiler on the top and the Neon logo on the back. You can also see my GRM Dork sticker when the light is a little different. Anything under the vinyl will show up. Anyway, I started with the top of the trunklid, just like I'd do any other flat surface but I made sure to keep the backing on the vinyl so that the closest I could get to the back of the trunklid was about half an inch. Once the top bit was on, I pulled a couple inches of backing off, held the vinyl on its sides, kept it tight, and brought it down over the edge. I should mention that the brake light and lock cylinder had been removed already. Again, working from the center, I gave it some heat to stretch it, and just used my fingers and the squeegee to get it to follow the shape.
Same thing on the quarters. I used heat to loosen up the vinyl and then just pulled it around until the wrinkles were out, working very small sections at a time.
If you have a section where you need to use multiple bits of vinyl or if you want to have an edge in the color, you can use the knifeless tape. Again, these seams are going to be visible so your job is only to make them suck less. Put the knifeless tape down and then put the first section of vinyl on. You're going to use the knifeless tape to put a nice clean line in the "under" layer of vinyl. Use primer on the edge that will become the seam. Like this:
Once the first layer is down, you want to go ahead and get it good and smooth and then pull the tape to cut it and put a good edge on it. Now, you put a second piece of knifeless tape on the vinyl. Like this:
Apply primer to the paint and to the vinyl up to the knifeless tape line. Lay your second bit of vinyl over top and get it good and flat. Then pull the tape to get a good cut on the top peice. And now you've got a nice overlapped seam:
If you try to butt them up against each other, it won't look nice at all and one or both will eventually shrink back a little, leaving a gap. If you overlap it and make sure you get good clean lines, it'll look decent and it won't peel back. If you can make that transition happen on a body crease or in a channel of some sort, it will almost disappear.
The best advice I can give is to get some material and just play with it a bit. You need to be able to see how much heat you can put in it before it starts melting and how much you can pull on it before it starts tearing.
