I had not worked out in a long time and did a hard workout today. I'm going back tomorrow but what can I do so that I'm not too sore?
Don't go too hard when you're just getting back into it. Besides that, protein and a good night's rest.
Nothing at all. You should have done cool down exercises for all the major muscles you used...mostly stretching.
I think i misread the OP initially. You just worked out today, so you're not sore yet, right? ...I wouldn't work out again tomorrow if you're sore all over. Muscles need time to repair. Something lighter may be ok, but i'd stay away from anything that requires moving around a significant amount of weight. You're risking injury otherwise..