If you are in a borderline zone (like me) it's best to put against a south facing wall or as close as you can get to that.

I live on the Sea of Cortez Central coastal Sonora, Mexico..so protection from winter winds is necessary but mild enough for sure. My issue is to put where in landscape ..among other trees ..as there is a lot of leaf drop and ..front yard or back what kind of shade will it provide..And it is lo desert....

There are some guys in Mexico at this forum, might have more local advice for you: http://tropicalfruitforum.com/

Guavas can stay small like a bush or become trees that will provide some shade, not as much as an avocado or sapote would though.