Do a search, there are multiple threads regarding 3-way installs.
With that said I just did a 4-way yesterday and have done multiple 3-way setups in the past. Personally I pull off all the switches, turn on the power, and figure out which is my line (hot) which should be the only wire with 120v. I turn the power back off then using a spare piece of wire to make a loop between the boxes (continuity) I figure out which wires are going from switch to switch and label them. Once that’s done the only wire left unlabeled will be the load (light) and I install the new switches using my now labeled wires.