When buying tickets it is really important to have a good statistical understanding of the show you are considering. It is vital to to know the numbers such as venue size, location, day, etc... but it there's something more that should be taken into account; what would you actually go to?
Whether a music concert, a play, a sports game, or any other ticketed event, you will always have the best understanding of shows and performers you personally are into. If you prefer rap music or country music, most likely you will have a better grip of that scene in the ticket industry and it is important to take advantage of that. Knowing the technical numbers is very important but if there is an artist who is currently exploding in terms of popularity it would be wise to take advantage of the buz and buy tickets for that particular show.
If you don't really attend many sporting events or interested in that very much it will be much harder to analyze how likely a show is to sell out and how much money you can make on that show. What I'm trying to say is to take advantage of the knowledge you already have and focus on buying tickets that are within your area of expertise.
Do not let this scare you away from tickets that you don't know much about because there is definitely big money to be made in many different areas, but it is harder to buy outside of what you know already. At the same time you want to careful to not buy tickets that aren't really that good but you have just heard about a lot. Exposure to certain events will make those events appear better just because you've heard about them more, this doesn't necessarily mean you will be able to profit on them. Do not let personal bias and the availability bias lead you to make bad buys. At the end of the day events with good overall outlooks and promising data for the likelihood to sellout is what you should base your buying habits on, but also remember to use what you know to your own advantage.