Here are a few tips I'll pass on from my experience.
1. Don't use tap water. Either buy bottled water or get a RO unit. After switching, I found my battle with algae diminish substantially, as well as frustration.
2. Lighting usually can't be transferred to a bigger system, so your initial cheap lights should do the trick. Just make sure you are changing your bulbs at the appropriate time. Invest in some cheap light timers to turn your lights on and off for you.
3. Stick with cheap Instant Ocean salt to start. Some of the best tanks in the world use it, so no sense in spending more on the get go.
4. Buy a refractometer. The cheap plastic items used to measure salinity can be way out. Mine was. This will last for years.
5. Look to buy dry rock and only a little live rock. It is a lot cheaper than store bought live rock, about the same as used live rock, but doesn't come with any bad things like aiptasia, flat worms, mantis shrimp, etc. How much you get is up to you, but realize that some corals come with rock attached to them.
6. Consider starting with soft corals like mushrooms or leathers. They are easy to keep, forgiving for a beginner, and usually less expensive.
7. Get a decent amount of flow going in the tank. This was one of my initial failures. Even in a fish only or tank with just soft corals likes flow. There is a new power head out there called Jebao. This seems like it is going to be the next big thing considering cost, and could easily transfer to a larger tank. Here is a link to a discussion about them:
http://www.reefcentral.com/forums/sh....php?t=2283598
8. You will need a decent skimmer. As I doubt you will have a sump, I'm not sure what the best option for your system will be and you likely won't use it on a larger system. Try to find something used is what I would recommend.
Good luck and have fun! Post a tank build thread and I'm sure you will get lots of help at each step.