I find having a good lead sheet very helpful, if I haven’t quite committed the guitar part and the lyrics to memory.
But I almost always end up copyiing the best one I find online, and creating my own. I have to make sure that the chord changes exactly line up the correct syllable in the vocals (in lots of songs, chords will change in the middle of a word e.g. Mad World). Many online lead sheets only approximate this, which totally throws me off the flow of the song, resulting in a huge train wreck for both singing and playing.
I also like to write in the count for things that happen in the middle of the measure/bar.
Here’s the first page of my Mad World lead sheet:
