The following article: "Break Before You're Broken" by Pat Sherwood is a good one, but I wanted to add a little more context and some useful tidbits as it pertains to our gym and programming.
1.) A lot of times we'll tell you "you should be able to do the first set unbroken". That is really a guideline to choosing your weight, not a strategy. For example, if you see 25 reps of a back squat at 95 lbs in the first round of a 3 round workout, that weight should feel relatively light to YOU. If asked to perform 25 reps without anything else added, you wouldn't blink. That doesn't mean that you shouldn't break it up as long as you can keep moving quickly due to the relatively light load. Last Friday we used this weight/movement for 50 reps between two people. Because there were no other movements with a high demand on the legs, Matt and I chose to do 25 unbroken each. It was not easy, but also didn't crush us for the next movement.
2.) Don't go to failure! I see this way too often. Especially on shoulder movements such as the strict press, ring dip, push-up and handstand push-up. Let's say you have 40 push-ups. You crank out 10 easily, then 8 and realize you need to break it up. All of the sudden, you are down to sets of 3-5 and quickly failing on the 3rd (no-rep). Don't let yourself get to that point of failure during a WOD, it's much harder to recover from muscle failure than to keep moving in smaller sets with short rest before failure. In this example, do sets of 2 with a quick break instead of trying to get that third. If you are working on your pull-ups, the same is true. You'll move a lot faster in general using singles with a two second break than you will failing on the second attempt every time.
3.) Changing strategy and weight in the middle of a workout is acceptable. Thing might not go they way you originally planned. Full article: Break Before You're Broken