As your strategy depends on your goal(s), you have to determine:
#1 Will you take ANY job that presents itself? If so, skip #2. If not:
#2 Do you have particular needs/desires re:
---geograpical location
---type of aircraft used (R22/300/ect)
---type of school (small/large/141/61/etc)
---what you want to do after your CFI stint
Once you have that ciphered, then check the want ads (here, JH, Vref, EFS and so on) to see who's hiring - somebody always is. If nobody advertising fits your (initial) desires, then find the folks who do, check their website (if they have one), learn a little about their ops, then call them. There's nothing particularly wrong with just mailing resumes, but you can bet that most of them will go right to the round file - a phone call might save the effort (of course the call may be more expensive then the letter...).
Hope this helps!