Simple rules that are true in 99% of cases and will save you some money:
1. Don't by names with more than 2 keywords (for most extensions, even limit it to 1)
2. Don't do brandable modification like xtreme on anything more than 1 word core. Meaning, xtreme.com is fantastic, xtremely.com is good, xtreme+word.com is most probably waste of money