First, decide which characters or teams you're most interested in. Then, search for reading orders specific to them. Some websites and forums dedicated to Marvel comics can provide detailed and accurate reading sequences to get you started on the right track.
Well, a good way to begin is to start with the key characters' origin stories. For example, Spider-Man's or Captain America's. Then move on to major crossover events and ongoing series. It might take a bit of research to figure out the exact chronological order, but it's worth it.