1. Don't Post on Friend's Walls - If they are your actual friends or they previously approve then it's okay. This can be incredibly annoying for the customer and might hurt your fan numbers, especially if they don't agree with what you post.
2. Don't Tag Everyone in Your Pictures - Odds are they really aren't in the picture, so don't do it. There's nothing worse than signing in and having to remove yourself from all sorts of party promotions. I have personally blocked people for doing this (after requesting they stop of course).
3. Don't Add People to Groups - Let your customers join themselves, no one wants anything shoved down their throats. Suggest that they like your brand or request that they join, but don't add them automatically.