What not to do?

Hey guys—this is my first post on the site so cut me a little slack if I make any mistakes or if this has been asked a million times; I'm looking for some advice on what not to do once someone has been swimming on their own for awhile now. I started swimming laps at my local pool in August 2018—so still fairly new—consistently about four to five hours a week. I've noticed huge gains in my technique, speed, comfort, physique, and am feeling pretty good with how far I've come on my own. I'm not in one now—but I want to avoid falling into a slump so I'm asking if anyone has any ideas on how to make sure I'm constantly moving forward with my progress/staying motivated. Basically I'm trying to not plateau—I want to make sure that if things are getting easier, that I make them harder before I get stuck in a rut of bad habits. I have a basic fitness tracker that tracks my metres, time in pool, lengths and I think speed? I'm not sure what the last thing I mentioned on my tracker but whatever it is I average 3'14"/100m. What does that mean and does it matter? What kinds of numbers should I be paying attention to, what matters/what doesn't, and what are some things that would be good for a somewhat new/usually swims in the fast lane/can do a decent flip turn kind of swimmer to do at this stage of the game? If this helps—I usually swim freestyle and will do some breaststroke. As far as goals go—I just love the feeling of a nice long swim and love how it's making my body look and feel. I think next year I would look into a race of some sort and am going to attempt open water training with a buddy on a kayak.