>>43273462Well, the way I solved it is making some combats more creative. Like, ok, you have regular combats with goons and some monsters, but in some others add some kind of gimmick here and there, like dropping the ceiling, or traps that are setting off in the middle of the battle. Another option would be using more interesting enemies, or enemies that have special attacks, or tactics, that force your players to think strategies. It doesn't need to be too complex, just one thing that would caught them offguard and they will have to reinvent themselves. Also, you could give them extra-difficult situations, like a combat with a higher EL only because there are too many monsters, or because the thing is too strong, forcing your players to either retreat, or to find some kind of advantage. With this solution, don't go hermetic about the rules: if your players ask you to do something crazy, go for it (while being reasonable about it).
For instance, I DM a game for my cousin and a friend of his. I DM "the return of the whiteplume mountain" or something like that, some old AD&D module that wizards addapted to 3.5. The whole thing was loaded with shitty encounters, and as I only had 2 players, they had more treasure than they should, and so they defeated most encounters with ease. So easily, that they underestimated their opponents. So, they got into one encounter with a Hag and some water monster, and the warrior got penalized strength and went unconscious, so they retreated, so the cleric could heal his strength the next day. As the monster were aware, the hag ambushed them during the night, and, instead of outright killing the warrior on one hit because of him being unconscious, the whole scene was a couple of rounds long, with the warrior trying to hold the hag that was strangling him, while the cleric tried to help him. The hag retreated, and the warrior got some new scars, and the dealt with the thing after healing, but more scared.