Are your tennis shoes too big/wide for you?
As long as your shoes are the right size, you then need to get the laces tighter.
Start pulling the laces tight near the toe of the shoe, and pull them tighter working your way up to the shoe opening.
Tie them tight and tie a double knot.
After your warmup, you will find the shoes have loosened somewhat. Retie them tighter.
After a while, they may again feel too loose.
Tie them tighter again.