I'm going to the US Open first weekend.
I've never been to a professional tennis match before -- any tips?
Which days? Also is there anyone in particular you want to see? Anyway here are some thoughts regardless
-I'd echo mir's advice but make sure you get an afternoon ticket and also look at Louis Armstrong afternoon tickets unless you absolutely need to see someone like Gauff or Djokic or Alcaraz in person - Armstrong is slightly smaller and also gets you access to all the outer courts, but it won't get the top top names. A grounds pass is still a great time, but often the upper level seats at Ashe are cheaper than grounds passes which makes no sense to me but whatever.
-I'd make it a priority to see both doubles and mixed doubles. Often you can see higher profile players on smaller courts this way, and there are usually great doubles matches on the smallest courts where you can sit where chum was sitting (but not with Sinner). Those small outer courts are in my opinion what makes an event like the open so great, because there aren't many settings where you can get that close to world class athletes competing at the highest level for that price.
-The order of play usually comes out the night before and I try to have a general plan of who I want to see, but sometimes I'll bail if a court is too crowded or the match isn't competitive, or I'll change it up if there is a match that is a potential upset or very close. If there's a match I really want to see on an outer court, sometimes I'll head over before the previous match is over to guarantee a seat or food seat for the match I want to see. Often outer courts will fill up, so be prepared to change it up if your preferred match is full! (Or wait for people to leave which only happens during changeovers)
-Having a friend helps A TON because there is no assigned seating and going solo can be a pain if you want to like get a drink and go to the bathroom if your preferred match is crowded.
-If your favorite player isn't playing a particular day you can try to see them practice although it isn't an ideal viewing situation and can be crowded for the biggest names. Not my cup of tea personally but could be pretty cool if you want to see them pretty close. I think those schedules are posted as well so you might want to plan around that, too. The practice courts are right next to some of the higher quality outer courts which is nice
-should go without saying but bring water and wear sunscreen. It'll be hot.
-Finally, depending on where you're staying I'd recommend taking the subway or LIRR, there's a stop more or less at the entrance. LIRR will be more comfortable and a little quicker but is way less frequent and a little more expensive and a little more of a pain if you aren't staying near Penn Station.