Try to stay in xp range, and farm bigger waves under tower. Ask your jungle to be nearby to deny a tower dive when farming a larger wave under tower. If you're sufficiently behind that enemy can dive you, they probably will. If your jungle has cc to lock them there you guys can probably get a shut down for free and alleviate a lot of pressure. If your jg is just damage, hopefully you can at least 1 for 1.
The more important thing is not falling that far behind in the first place though. I never understand how someone dies 1v1 in lane at level 2, or twice or more before level 6. Don't all in if you don't know you can win it for sure that early on... and once you've died once play a lot more passively...