You should start with the mic: pick one that has the sound you're looking for.
You only have one mic? Learn what its characteristic sound is, and then apply the effects to change it to what you want.
Or buy another mic that has the sound you want.
Or a preamp that complements the mic you have already.
Or...the list is endless. The fact is, that EQ and compression don't make a poor sounding vocal anything but an EQ'd or compressed poor sounding vocal.
Another strategy is to TRY THINGS OUT. That's what all of us do. The singer in my band LOVES the "Vocal Presence" Reverb preset in Cool Edit Pro 2.0. He's thinks I have some magic that makes his vocal sound wonderful, when his own recordings don't do it for him.
It helps that I have a condenser mic that works very well on his vocals in the room I record him in...but I wouldn't have discovered that combination without patiently sitting at my computer and listening to his vocals, over and over, until I found the sound he liked.