A long time ago, I came up with a nifty little sheet. Well, OK, I didn't come up with it, I altered the one in the DM's Helper book and I still use that.
It has spots for HP, stats, saves, gear, ect ect ect. I also has some areas that help me keep track of time.
See, my players write down what they think the damage is that they took, and I write down what it really is. We've had the barbarian drop suddenly, and the mage scream all through the battle that he was getting butchered.
It's not that I don't trust them, but they get excited during the combat sometimes, and the honestly forget to write something down. I, on the other hand, keep close track of everything.
We roll to see how many arrows fired get broken or destroyed, we keep track of how many days rations did salt-curing that wild boar and finding that patch of wild potatoes add.
But, we do it seperately. I keep track of decay, and what the HP totals really are (one game we played, all they had was name, gear, and spells written down, I kept track of everything else) and how well they are doig.
My little cheat sheet also lets me keep track on initiave.
Short version of the rambling BS?
Create a DM Cheat sheet. Use it. It works. Update it at the beginning of each session.