Best ways to improve as a chess player?

I'm a relatively new chess player (began last fall) and I just thought I'd ask for a little input from more advanced players on the best ways to improve. 

There are tons of different activities that help to improve your skills like tatical puzzles, analysing GM games, analysing games you lost, studying theory, just playing chess, etc. However, I'm not entirely sure which activities are the most beneficial. Are tactical puzzles really that helpful? Would it be better to just play chess and solve puzzles you encounter in an actual game? How important is theory? Does the analysation of GM games really benefit a ~1500 rated player? Which activities are really the most important? I'm familiar with most openings (ruy lopez, king's indian, italian, sicillian, etc.) but I still have a ton of theory to learn. What would you recommend to someone of my skill level? What should I be spending most of my time on? What helped you the most?

Thanks in advance!

I know a lot of people tell beginners (I'm sort of a beginner) to avoid theory. But how valid is this? In my experience learning theory and studying popular openings really helps to avoid traps and common opening mistakes that are hard to forsee tactically. I think it really helps to understand the ideas behind the different openings. It helps with both defending and attacking. Thoughts?

If I had to single out one best way to improve, I'd say playing OTB games.

If they're at long time control and you can analyze them with your opponent and/or strong players after the game, that's a plus.

It's not an either/or proposition : it's a question of balance.

One of the greatest improved players I know of - and he increased in greatly in strength in middle age, swears in playing through master games. He's not on his own. Many others recommend this method. Typically covering the moves with card and working through slowly, trying to work out the next move. Visualising what the position could look like in a few moves.

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Yes, I've definitely found that slow games help improvement a lot more than blitz. I think blitz is more or less an upfront test of your current chess knowledge and skills while slow games are more of a problem solving test and deep understanding exercise. That's where improvement seems to be made.

Yes, I think a mentor is definitely one of the best ways to improve.

I took a trip to Washington, DC last year to visit family and of course looked for local chess clubs. I found the Arlington Chess Club and decided to see what that was all about. It turned out to be huge. The only other club I had been to at that point was at a local town with like 3 other people. So I was super excited to walk in and see dozens and dozens of chess players. I felt like I was at a tournament.

Anyway, my brothers and I weren't members there so we couldn't play the ladder. We just kind of hung out and played games with each other as well as a few other guests. After handeling some responsibilities the club president went over to our table and played with my brother. He beat him several times and then invited us into the "chill room" where players can have a quite room to play casual chess and dicuss games. We all played him several times and dicussed the games, different openings, positional questions, etc. It was a really nice experience and I really learned a lot. Just from that one experience I found that my games were improving. My analysing positions together it helped me to grasp a deeper understanding of how to build a strong position, develop my pieces properly, etc. If I had someone like that helping me every week then it would vastly help my improvement. Unfortunately (although it does feel good) I'm the best player at my local club that started up a couple weeks ago. So I'm doing the schooling. :P While it feels good to "rule the roost" I really wish there were people there significantly better than me so I could have a mentor. BTW the guy in Arlington was rated ~1900.