We will cover picking out lights, controlling, powering, and different techniques for hanging them.
Step 1: Ordering your LEDs
5050 - This is the type of LED. This is a standard part, it's big and bright but still runs cool. It's common to see 3528's in LED strips, avoid these, they're a lot smaller and dimmer. To go bigger than 5050 you're going to get a lot more expensive and a lot hotter.
RGB - Red Green Blue. This means it's a tri color strip. By mixing the different colors tri-color strips can do any color in the rainbow.
5M - 5 meters. This is the longest length I've found. You can use it pretty fast, go any shorter and you'll pay extra.
300 - The count of LEDs. The most common setups are a 5M strip with 150 LEDs or 5M with 300 LEDs. I recommend the 300 count ones because the price difference isn't that much and they're a lot brighter.
If you don't want to search around this set should get you started, it comes with a power supply and controller.
So, to recap:
Search Amazon or eBay for 5050 RGB 5M 300 and pick one. I've never ordered from the same place twice (I always forget) but I haven't had any issues with any of them. All of them have been about the same. The only thing I would recommend is if you're doing a large room, order all the LEDs at once because the whites can be slightly off. In my living room one set of strips has a warm, pinkish white and the other set is a light cool blue and it drives me crazy because I'm picky about those things. Order your LEDs all at once and they'll all match.
For large areas like a porch it might make more financial sense to order a single color. White is a good for general lighting. Red and blue are very dull, don't count on them to provide more than an accent lighting.
I like the waterproof LEDs simply because it makes the strands easier to work with. They have a nice weight and flex more easily, plus the coating helps prevent shorts when mounting the strips with staples or other metal fasteners. The weight can be a problem if you're hanging them off the bottom of something and you want to rely on the built in tape, but other than that I don't see any downside to the waterproof strips.