Bathroom:

Well, the people who renovate your bathroom had better be pros, so no biggie there. A few things to think about though... if you have plastic carpeting on the walls, make sure to pick one without any lines in it. it will be crooked, otherwise.

Also, if they say 3 weeks, it will be at least 5.

Kitchen:

I haven't actually done this for myself, so no great advice here... but one thing you should probably remember is that you figure out how many electrical sockets you need, and then you double that, because everything runs on electricity these days. Also, don't put the stove in a corner or anything. That is very impractical. Make sure you design the kitchen the way you want it, because it is a bitch to change afterwards...