hi-
First off all there are a lot of different model of laptop on the market and most of them are not meant to be repaired (most of the time the motherboard dies and if its 4-5 year old, you probably can't come around one )
Hence if you still want to go down that road:
When i want to repair one, i google the model + service manual and hopefully find a manual to repair it.
Then, when i put it apart: i draw and take notes to put it back together....
good luck