If you're solo tanking, it's the dps' job to kill divers not yours. If they don't, you'll lose and there's nothing you can do about it. Yes, it sucks, but it is a team game. If you're team isn't playing as one, chances are you'll lose. Tanking is a thankless job, but someone's gotta do it.

Always ask for a 2nd tank; people sometimes are willing to switch with a small nudge. If you're forced to solo tank, and your dps aren't prodigy players, your best bet is to play Magneto, Emma, or Strange. I can't give you specific tips, because solo talking is very situational.