This post focuses on the process of getting the vocal chain right for the given performer.
The signal chain for vocals is probably one of the most important production choices in pop music. Of course, it helps to have a healthy selection of devices to choose from. Every voice has unique qualities, some of which should be emphasized and some of which should be de-emphasized. The tools available to accomplish this are, in order of affectiveness: microphone selection, mic placement, and preamp selection.
Since mics have the most influence on the sound, I recommend that you start out by lining up your microphone selection on stands, all routed through more-or-less the same signal chain (such as the stock preamps of a mixer). Write numbers on some post-it notes and have the performer place those post-it notes on the mics in a random order without your knowledge. Have the performer sing the same phrase through each mic in numerical order at about the same distance and, as you’re doing that, adjust the mic preamps so that the level you are hearing is consistent from mic to mic. Listen for changes in tone and response that compliment the voice. Make notes as to which numbers you like and why. Then go through a second pass, adjusting for mic placement (if one mic sounds too burly, try having the performer move back a bit, for instance). Eliminate the mics until you have the two or three best left standing. You may be surprised which mics you liked the most! The blind test is useful so that you don’t go into the experiment with prejudices. Sometimes the best mic for the task is a simple SM58!
Next, try a different mic preamp that seems to make sense for the overall tones you’re hearing. If the sound needs beef, try a preamp with a transformer such a Neve clone or the like. If the sound needs smoothness, try vintage style tube pre. If it needs clarity, try a transformerless preamp. Or, you can try using an emulating preamp such as the Focusrite Liquid Channel to get a general idea of what you’re looking for. Again, note the differences in tones and the mic/preamp combinations that sound the best. It might help to track these takes for reference.
Then, once you’ve found the best combination, add EQ and compression to taste, if appropriate. Make sure that when fects you’re being conservative and that it actually makes a noticeable improvement in sound. Don’t just add things because you can.
Hopefully you’ve now found the most pleasurable combination of equipment for the performer’s voice. If you haven’t been successful at finding a good solution, you may want to investigate renting a microphone based on what you know about the given mic from research you’ve done. This is generally a shot in the dark and may not be worth the money. It’s unusual to walk away from this kind of test disappointed, however. Usually there is a solid consensus on what sounds best between the performer and the producer even when choosing between just a few mics and preamps.