There's nothing like a bunch of suds to leave your glass full of streaks. This isn't a problem if you're using vinegar or straight glass cleaner -- no soap there. But if your coffee table is truly dirty and you're adding soap to the solution, remember: Go easy.
It doesn't take much soap to get rid of that dirt, and using too much will result in an overly dense cleaner that can leave a streaky residue on the glass.
And speaking of residue: It's perhaps the biggest glass-cleaning mistake so many of us make.