Salary negotiation is a tedious and daunting task for any professional, never mind technical professionals.
The thing about negotiating your salary is that it's more of an art than a science. After all, aim too high and you lose the whole thing by looking unrealistic and out of touch with the current market. Aim too low and you can instantly throw away thousands of dollars each year.
Failure to negotiate properly is equivalent to going to your bank, taking out a few thousand dollars, walking out , throwing them in the middle of some street and then standing there and watching as people walking by take your money.
Salary negotiation starts the moment you get a call for a new job.
If you're contacted by a recruiter or the actual hiring company, then somewhere early on in the process they'll ask for your salary requirements.
What you're really aiming for is a nice 10%-15% raise for your next position. Some get 5% and some get 25%. 15% is a conservative number that plays it safe. Just remember that usually salaries are progressive. They do not jump by 100% every time (usually.) This also means that the higher salary you receive this time around means the higher potential salary you will receive the next time also. It compounds over time.
Most likely, if your prospective employer needs you more than you need him/her then you might be able to keep that 15% raise. However, if you need them more than you might negotiate down to 10%. The Main point is that you restrict your range so that you're talking $100s rather than $1000s.