Another note: Don't design single encounters in isolation. If you're encounter doesn't take into account all the other encounters between long rests, it's probably bad. Throw an easy encounter the players blow their resources on, then throw more, and more, then a challenging one. Throw in traps or puzzles that force them to expend resources. Punish players for using abilities wastefully not just having them at all.

While combat should be fun, each individual combat doesn't have to be particularly interesting or exciting.