things that will give you better reception:
-more than 50% battery life
-external antenna instead of internal
-not being inside a building
in general though, unless the phone has a very small or badly placed antenna you will not see much difference. some people claim nokia phones with an external antenna work better but its just a matter of opinion.
in regards to data:
-2g phones will have better reception but slower speeds since a new phone would rather connect to a weak 3g signal than revert to 2g.
all that said, if you live on the edge of a dead zone you are pretty much screwed unless you want to swap providers. all the tips and tricks in the world will not fix that. you can try the two things i list below which might help, but dont expect miracles.
-update the list of cellular towers on your phone. i got an extra bar this way intermittantly.
for external antenna phones only:
-get a piece of bare copper wire about 12" long and wrap it around the antenna, effectively extending the antenna. i've seen this give enough signal boost to make a call, but it also probably increases your risk of cancer.