Do I let the car pass first until it's clear and will it slow down so I can safely switch?
Judge it by how traffic is flowing. If the other lane is travelling faster than you, let it pass, then slip in behind.
If the other lane is slower, then chances are you will pull ahead in a few more seconds, and have space to change.
There is no hard and fast rule, but someone has to be moving slightly faster than the other person. If the other guy isn't falling back and you don't have space to speed up, then you need to slow down slightly and slip in behind him. We are only talking about a couple of mph speed difference. Don't do anything silly that disrupts traffic flow, and plan your lane changes well ahead of when you NEED to change.
Ianab has it right, but I'll throw in a caution. Keep an eye on the other vehicle. There are many drivers who ride beside other cars because they aren't paying attention to their driving. They simply match their speed to the other and don't have to worry about mundane things like checking their speed, etc. If you increase, or decrease your speed a little, they will match it and not even know they are doing it. (some tailgate the same way!) You may need to do something more radical to get their attention like a quick burst of acceleration, or braking (makes sure it is safe to do) I found that if you do a sudden 5 mph change, it usually breaks their lock on you and they either pass, or fall behind.
I've gotten tailgaters down to 45 in 70 mph zones by slowing my 18 wheeler gently without any brake lights. (When it wouldn't interfere with other traffic.) When they finally realized how slow they were going, they'd fly past and often tell me I was number one, by holding up their hand with the middle finger extended. I'd wave back, smile at them and then speed back up to my normal speed. (I always resisted the temptation to tailgate them to show them what it was like, because I knew that if they panicked, it would have scratched the chrome on my bumper!)
if there is a car in your blind spot, you are not blind and obviously it is not safe to switch lanes until there are no cars in the lane you are passing. You can't control others but you can slow down or accelerate to avoid the conflict.
It is YOUR responsibility to make sure it's safe to change lanes. If there's a car so close he's in your blind spot it clearly isn't safe to change lanes. So you don't change lanes.
Well, you need to ensure that you're clear and signal your intentions to change lanes so he knows what to expect. You can either slow and let him pass or speed up to get clear. Which one usually depends on whether you're changing lanes to prepare to exit or changing lanes to pass a slower vehicle.
You don't wait for the other car to act. YOU are the one in control and can either slow down or speed up to get away from the other car.
You either allow the other vehicle to pass, or your accelerate to a point where you can see the vehicle in your rear view mirror to safely switch lanes.
turn your signal on. If they don't slow down to let you go then you need to speed up or slow down until you can get over.
Let him pass because he's too close.
A thought shared.