Plosives are your enemy!

Plosives are the popping sounds that happen when you sing hard consonants like P, T, K, B, D and G. The closer you get to the mic, the more of a problem they become.

That's why they make pop filters and why most dynamic cardioid mics are designed to increase the bass and decrease the treble the closer you get (aka the Proximity Effect). Of course, this also makes your lyrics harder to understand.

Oh, and do you know who was using that mic before you? Are you sure you want to put your lips on that grille?

Prioritize soundcheck and work with your sound engineer to find the right mic placement and monitor levels. Then make sure to stay in that spot during your performance. The Mic Trainer can help with that!