Should I always be going 100% or is it better to do 70% one set then maybe 80% for the next?
Damn. And the nerd in me got all excited about a math question I could possibly answer.
ALWAYS go 100%.
1 rep of everything is all you will ever need. Since when, in the real world, does anyone lift anything more than once? If you need to get a car off of a baby, you do it once. If you need to pull your buddy up from a cliff ledge, you do it once. Don't let science tell you otherwise.
You do 1 rep of everything, then walk out of that gym feeling like a man. Punch a hooker in the tits on your way home and your day is complete.
Before we all write this guy off as a loser, he may simply be asking about ramping weights, pyramiding, etc. After all, we sometimes forget that this is a beginners forum.
If this is your question, the short answer is that there are many different choices to make here depending on your goals. Typically one will start at a lighter weight for any particular lift, and ramp up to the max you can lift for X number of reps. 5/3/1 is an excellent example of a program that adheres to this principle. Do a search.
LOL. Not writing him off, just goofing a bit until he gets a chance to get his ass back here and expound. After all, I may still have a chance to unleash my inner nerd, you never know!