How do I determine where to start each weight at?
From the Starting Strength Wiki FAQ:
"The weight you use is going to be determined by the amount you can do for 5 repetitions with proper execution and technique.
The way the "first day" is explained in Starting Strength, the trainee warms up with the bar, then adds a bit of weight and does a set of 5. The bar speed will be identical from set to set. Continue to add weight and do sets of 5 until the speed of the barbell begins to slow.. Keep the weight there and perform 2 more sets with this weight. That is your first "3 sets of 5" workout for that exercise.
Yes, this is low. It allows for a certain fudge factor that is present when dealing with a novice's ability to evaluate his own technical performance.
Generally, if a newb says "I benched 135 x 5 for the first time, my technique was great!", what he really means is that "I benched 135 x 5, but I probably should've only used about 120 or 125"
Be on the safe side, start lighter than you think you need to, and go from there. This also helps develop a base of conditioning with slightly less weight than absolute max, which helps reduce initial DOMS.
Let me say that once again.
Start off using weight that is LOWER than you think you can handle, and progress upward. It is better to use weight that is too light than weight that is too heavy."