To set up the tank itself:
0.5- Choose an apropiate location for your tank, away from direct sunlight, heat radiators and A/C outlets, but close to a power outlet.
1- Make sure the floor is strong and level.
2- Make sure the stand is strong to hold all the weight.
3- Put a layer of styrofoam beetwee the tank and the stand. This will help to reduce stress in the glass in case there is a imperfection in the stand surface.
4- Put the tank on top of the stand (have someone to help you) and look at it. If you like it, then it's positioned.
To set up decoration:
0.5- Make sure you know what you want to put there.
1- If you are going with an UGF, set it in the botom of the tank.
2- Pour the gravel.
3- Put your decorations and place them where you want them.
4- Set up any air hose and secure it to your glass or decorations.
5- Once it's all set, fill it with water slowly to avoid disturbance to the set up.
Filters:
1- Set up the filter(s), pumps, and make them run.
Before adding fish:
1- Do your cycle.
That's pretty much a rough list of taks. You can fit some other in beetween, but this is it. About the stupid mistakes you say, I don't know what you did before, so I can't tell you what not to do.
In the newbie forum you can find a more detailed guide about setting up a tank.
