I got my left nostril done about six years ago, when I was 30. The initial healing had some minor problems, but since then it has been trouble-free. XJET GIRLX and the website suggested by 11811 (especially the ‘aftercare’ section) cover many of the points I was going to bring up.
This might go without saying, but absolutely do NOT allow anyone near you with a piercing gun. The only way to do a proper piercing is by hand with a sterile, sharp hollow needle. It is a good idea to visit a few piercing places and talk to different piercers to make sure you are comfortable with their cleanliness, quality and professionalism.
IIRC, the cost was about $60 including jewelry. The nostril screw will be straight to start with (a plain surgical stainless steel stud is probably the best choice). The piercer will measure your nostril and bend the stem with pliers to fit your nose. After the piercing heals, you may need to get the screw re-bent or trimmed to fit better once the swelling goes down.
The hardest part is simply leaving the piercing alone when you’re not cleaning it. For at least the first year, NEVER touch the piercing without first washing your hands thoroughly. And make sure that your piercer welcomes follow-up phone calls or visits if you have a question or suspect an infection.
Before getting pierced, get plenty of rest and take your vitamins. I caught a very bad cold the day after getting my nostril piercing, and it was uncomfortable to say the least. But, it also taught me that blowing my nose with a nostril piercing isn’t much different from blowing my nose without one.