Remember to stop at positive failure (the last rep you can complete on your own) or at most get just a little help completing your final rep.
I do not advise going to the point of forced reps where your partner is assisting you in completing the last 2 or 3 reps of a set.
Once you complete 6 reps on your own with good execution that is your cue to add weight. If you are doing forced reps you will not have a good indication of when to increase weights because you will be using more weight then you could actually handle on your own in the desired 4-6 rep range.
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