1) Location, Location, Location. Site your receivers. If you can get them close to the stage, with a good line of sight, do it. In the wings, or in the orchestra pit on risers so they at least foot level is great. Audio snakes are cheaper than antenna boosters. But if you can afford antenna distributors, do those to...if nothing else, they make it a lot simpler to set up and strike.
2) Location, Location, Location. The best sound is from the forehead, just under the hairline. If the actor is wearing a wig cap, run the cord under it. If they have thick hair, bobby-pin the cord to their hair; near the back of the head, and near the top of the head so it doesn't flop down over to one side. Bobby pin or tape at the forehead. Don't be tempted to pull it down until it looks like an Indian Caste Mark -- it will do what it needs to do from hidden within the hairline.
The second best sound is along the cheekbone. The temptation again is to run the mic directly towards the mouth and tape it on the soft part of the cheek. Don't. You get nasty resonance you will have to notch out. Keep it up on the cheek bone and use the natural planes of the face.
For a really, really weak voice, invest in something like a Countryman E6 and use the boom to place it just outside the corner of the mouth.
3) Location, Location, Location. The most comfortable spot for most actors with dance or heavy physical movement is the small of the back. Use or create a microphone pouch with a wide (1" or better) elastic belt. Stitch a pouch that holds the transmitter and velcros closed. Have the actor wear the belt high and snug, just below the rib line. But be guided by the actor in this; they know better than you what their role demands and what will keep them comfortable on stage.
4) Location, Location, Location. Put the sound board where you hear what the audience hears. Try not to be under a balcony (because there are strange room nodes under most of those), try to be in the area covered by the main speakers. If you have any reason to believe the coverage is uneven, get up from the board several times during the tech process and take a listen from different parts of the house.
It is just barely possible to mix on monitors. My preference, the few times I've been forced to it, is to set up a binaural pair in the house and mix wearing earphones. Simply monitoring what you are sending to the speakers does nothing; you need to hear what the sound in the building sounds like (well, unless you are a million-dollar rock show...but that's a whole different game). At the moderate levels of theatrical reinforcement some portion of the sound will be direct acoustic -- if nothing else, the stomping feet of the dancers and leakage from the orchestra pit -- and you have to blend your input with that.