play and listen
think of your theory and experience (most songs aren't complex, most songs just follow the theory very nicely)
You don't really know unless you can analyze the song itself and match it up to the tab to verify it. For example all the tabs on UG for Iron Maiden's Aces High are wrong in some way (wrong intro or missing harmony guitar or wrong chorus chords, etc.) but combined together and taking what is right from each you can piece the song together correctly.
Quote by dale-banez

my gear:
oh wait, no one cares

Quote by uncboy19
man all guitars are female. if they werent you couldn't make sweet love to them with your fingers. ok somebody better quote that ****. thats like quantum guitar **** rite there.