Pretty much stop fighting one mob at a time. If you make full use of a judged Seal of Wisdom or a judged Seal of Light (these are situational, pick the one that works best for how you're doing) you'll often end up coming out in better shaoe in either health, mana or both than you would fighting just one mob.
I tend to make slow fights more exciting by trying to take on as many as I can - then you're looking at your seals closely, looking at your health, you may have to bubble and bandage, etc. But you'll constantly surprise yourself at how many you can take on if you push yourself.
Except with casters... casters kill.
Also, if you're only taking on one or 2 mobs at a time for questing or something, wear a spell damage set instead of your tanking set.