1) Get a qualified, experienced, native-speaking TOEFL coach (from your local college or English center)
2) Have the coach evaluate your specific TOEFL strengths and weaknesses by reviewing the report from ETS after you've taken an official practice TOEFL here: TOEFL Practice Online
3) Study the Official Guide to the TOEFL* by ETS under your coach, supplementing that with specific practice sets from the Longman TOEFL book in your weaker areas.
* Other good books to study are: Northstar, Bruce Rogers, or Cambridge.
4) Take the TOEFL practice test again to see how much you've improved and to identify any last minute chances to tweak your skills.
You'll need about 4-6 weeks to prepare properly, and generally the available TOEFL test dates are about that far away when you login to register at TOEFL: Home. Best wishes.