I gave my son my old iPhone when my employer supplied phone was replaced with a new iPhone 4S. He called me to say that he had cracked the screen "a little" when he dropped it while sitting on the sofa.
The screen was cracked heavily on this phone. It made removing the glass from the mid frame a little more difficult but I just kept at it and eventually had it all removed. The guides were very helpful and I watched several YouTube videos to get an idea of the best way to proceed. I took my time but only spent about 45 minutes start to finish.
Just be careful of the small shards of glass if your screen is cracked badly. Go slow and be methodical. Don't force anything. Oh yeah, have fun! I did.