Just using higher damage/lower hit point monsters is probably the best advice. Hobgoblins are
better than gnolls, for instance.
Personally I hardly ever see 5e combat take more than 4 rounds, and those rounds go reasonably fast, so I don't think it's a huge issue.
If your turns feel slow then probably speeding up player turns is the main thing for more exciting combat, so avoid anything that is making them hesitate, like 3e/4e style square-counting - "close enough is good enough" should be your motto, and don't be tied to the grid.
better than gnolls, for instance.
Personally I hardly ever see 5e combat take more than 4 rounds, and those rounds go reasonably fast, so I don't think it's a huge issue.
If your turns feel slow then probably speeding up player turns is the main thing for more exciting combat, so avoid anything that is making them hesitate, like 3e/4e style square-counting - "close enough is good enough" should be your motto, and don't be tied to the grid.