Work slowly, and double-check components before installing.
These projects are typically not difficult to assemble. The stink of the process is that one missed connection, shorted wire, or incorrectly-installed component can make the whole thing not work. Therefore, don't get frustrated if a build doesn't work correctly right away -- plan that you may need to do some troubleshooting (it's part of the process for even the most experienced DIY builders).
Be methodical, and be patient. All will be good.
If questions come up, there are some great places to seek advice. Most folks over at
DIYStompboxes are helpful and friendly to newer builders.