Choosing an advisor

Recently, I've been in touch with many students in the process of finding a PhD advisor. While it's not impossible to change advisors, it usually comes at the cost of more time spent in the PhD program. Here's a list of things you can do to improve your chances of finding a good match:

For each potential advisor X, do the following:

1. Make sure you don't have a problem with X's research interests.
2. Make sure you can get along with X.
3. Talk to X's current students about X's pros and cons. Ask clever questions since many students refrain from discussing the downside of their advisors with a stranger. Don't forget to ask if X is too (dis)engaged with his students. This step also helps you find out more about your potential academic siblings.
4. Find out what project would fund you. Is it a long-term or a short-term project. If it's a long-term project, make sure you like it.
5. Find out if X has a tenure, in tenure track, or neither. Non-tenure (track) faculty are more inclined to leave their academic institution and find a better position somewhere else, which is -usually- a bad thing for their students. Tenure-track faculty are more inclined to work harder, and tend to be more demanding (which can be good or bad, depending on who you are). 
6. Collect some statistics about X's research group. How many students does X advise? A very large number (e.g. fifteen) usually means X won't have time to interact with you, and a very small number (e.g. zero/one) usually means X has problem with funding (or a new hire). Find out what's the average lifetime of X's students in the PhD program; the variance is usually small. 
7. Find out if X collaborates with other academics (inside or outside the department/school). More collaborators usually mean a well-connected advisor, which can be very useful for your marketability.
8. Find out where does X's graduates go.
9. Meet with X. Ask smart questions. Be ready to talk about your previous work.

If feasible, do a research project (e.g. in a lab or a regular course) with your preferred advisor before committing to be his student. You might change your opinion after working with him/her for a while.