You mean, other than for me to threaten to stick a red hot poker in your eye if you use it? :)
BGA isn't "impossible" for a hobbyist. But it's a huge amount of work for very little gain.
All advice here also applies to what people refer to as CSP (chip scale package) as well.
1) BGA packages generally require better than normal PCB rules in order to actually "fan out" the signals to routing. BGA packages can put a lot of signals in a small area (that's why people like them), and you wind up needing very small pitch traces and vias to get everything out. You may even need an 8-layer board to pull it off
2) You can't really inspect BGA without X ray equipment. I don't know of any hobbyist X-ray machines yet (that actually might be a good project...)
3) BGA is prone to strange failures if you don't get ALL the balls down properly. You can get things like unpowered chip sectors because a Vdd ball is a little flaky (chip manufacturers don't always spend money reinforcing the on-chip power grid if they think you are using balls).
4) If you have a "small" (less than 40 pin) BGA, there is almost always a QFN option that is easier to work with and is almost the same size.
5) Thermal management of a BGA can be tricky. There is normally better heat flow out the top of a chip than down into a board, but BGA's normally want to push heat into the board.
That having been said IF YOU MUST use a BGA:
1) Use a contract manufacturer
Really. This is the best advice. I got some very tiny CSP chip boards done for like $50 per board for 20 boards. Even if your time is only worth $20/hour, the crossover point is 50 hours of work. You'll spend lots more than that if you're playing with BGA.
2) If you have a small number of balls, see if you can adjust the footprint such that you can hand solder things by having copper stick outside the package outline.
I can't give you any general advice as this is specific to every chip. However, I have successfully routed things like power regulators which only have a small number of balls this way. I have also routed some bigger things like FPGA's this way (you can reorganize the output pins) where I simply didn't even try to use any pins not on the outermost edges. However, you are at the mercy of the manufacturer as to how many power balls you need hooked up properly.
3) Use a reflow oven. There are lots of reflow oven things on the market for <$500. If you get things placed right, a reflow oven gives you decent results.
4) Don't try to hand rework. Accept that you're going to throw the board out if there is a short.
Yes, I'm sure lots of people have done things and been successful with BGA. However, if you do enough, you will find you are at the mercy of luck rather than consistency with BGA unless you let folks who have reflow and X-ray machines do the work.