I have been in many church worship services where you can hardly hear the lead vocal. To tell you the truth, I have even led some of these services.
There are many causes to this problem, so let's go through the chain of events so you can get your lead vocal sounding amazing.
This may seem obvious, but the first thing you need to check is if the lead vocal is actually projecting. In worship, you often come across people who have little to no training or experience, so they have yet to discover how to put the 'umph' behind their singing voice.
Generally, they just need to learn proper breathing techniques or how to open up their throat and let the sound move freely.
Not all microphones are created equal. Yet, we often give every vocal the same one. I like to have three different microphones on hand: Electro-Voice N/D767a, Sennheiser e835, and the good ole' Shure SM58. When I bring a new vocal on the team, I have them sing the same chorus of a song, with the band, on each microphone.
The mic that sounds best wins the prize and is assigned to that specific person. Keep in mind, you should level the EQ on the soundboard before running this test so you have level testing ground.
Don't forget about the importance of microphone placement.
You should address this before testing microphones as microphones react differently depending on how close or far away it is from the mouth. The microphone should be no more than 1" from the mouth. Also, never put your hand over the mesh part of the microphone.
Have you ever moved around EQ knobs without really knowing what you are doing? I know I have. And it usually just makes the situation worse.
Luckily, it is not as hard as you might think. For tips on how to EQ vocals, check out this post:
Vocals have a wide dynamic range. To get a lead vocal loud enough to cut through the mix, you will often have problems with it getting too loud during bigger parts of the song. So, you can either memorize when these louder parts are coming, or invest in your best friend: the compressor.
Basically, a compressor narrows the dynamic range so you don't have to worry about it poking out too much, but you can still get those quieter moments to cut through. Here are some baseline settings for vocal compression to get you started:
To learn more about compression, see How to Set a Compressor for Vocals.
You are well on your way to making the lead vocal sound amazing. It will definitely take some work, as every sound system and vocal is different, but don't give up.