Soloqueue Surrender Conditions

(This is predicated on the condition that you are already getting stomped.)

As long as your team isn't raging at each other, then fight the game out, especially if you have some turrets to fight under. I've had quite a few games turn when the enemy team over commits to a fight under a turret (yes, even Nexus turrets) allowing our team a chance to get back in the game.

Doran's Items vs Wards

If you are at the fountain and your inventory slots are full and you still have a Doran's item, think about what your team needs right now. If it is wards then sell your Doran's item and pick up a stack of wards. If you know a fight is brewing and those extra stats will come in handy for that then keep the Doran's item.

Overconfidence

It is great that you are fed. Hi-five. Go you. Stop running straight up Mid without the rest of your team and dying to 3+ man picks. Get the rest of your team together so they can ward and act as meat shields while you do work.

What to defend

Your Mid lane turrets are more important than your Top and Bot lane turrets. If you have to choose between the two let your Top and Bot lane turrets go and stick with your team to defend Mid.

Lux

With Final Spark Lux has always been pretty good at sniping objectives, sometimes even blindly. Now that she can detonate Lucent Singularity when she wants she is even more of a headache when trying to secure objectives such as Dragon or Baron.

Really important to pull dragon out of the pit and ward behind it if there is a Lux on the enemy team.

Unfortunately, you can't pull Baron out of its pit, so you have to rely on wards and/or send someone out of the pit to harass her so she can't position to pull off a steal.