If you're a reading/visual learner, pick up Swim Smooth's book. It has taught me to get a solid freestyle stroke as a beginner after 20 sessions in the pool. Plenty of photos in there too to grasp a visual understanding of concepts.
If you don't savvy reading, consider getting some swimming lessons.
This video came from swim smooth and I really recommend the book.
Starting your swimming with this info helps you not make bad habits you'll have to break later!
Bunch of tips.
1) I like Swim Smooth videos/ book/ website. Its meant for the adult swimmer trying to get to the next level. Perfect for the 2:00/100 swimmer. Their "swim types" framework is a great way to quickly identify top ways to improve. Keeping your head down so your legs dont sink is a big one. Having the right catch (EVF) with no crossover in front of your head is another.
2) When I learned to swim a long time ago, they taught an "S" pull, where your hand goes under your body. It was complicated and led to injury. These days, they teach a simpler, straight-back pull outside your body with an "early vertical forearm" (EVF) catch. I use(d) Finis Agility Paddles with a PB every swim to reinforce/teach this proper pull technique...and its helped a lot. The paddles fall off if you're not doing it right.
3) After warming up, break the swim up into shorter intervals of 50/100s with some rest where you swim strong and with good form. Swimming long continuous distances can "lock in" bad technique. Have some consistent sets you routinely do (e.g 8 x 50 on 1:20) where you can track your time and improvement (use the pace clock).
4) I found that doing some focused strength training on the side accelerated my improvement. Upper back (traps, shoulder stablizers) helps lock in your catch...its not just technique but you need the strength to keep doing it without slipping. Work on core strength if you find yourself "falling apart" after some distance or if swimming is much easier with a pull buoy. Your core holds your body position. For me early on, I also found that my legs would cramp up after about 1500. I thought is was hydration at first but lo and behold doing some leg strength work made it go away.
5) Swim consistently. Just show up 2-3x week, get a fixed distance in (like 800m for a month or two, then increase). Use the clock to keep track of pace and/or get a swim watch. There's always someone who will be faster than you in this sport, just worry about yourself and celebrate when something small gets better.
Hope this helps. Good luck!
Technique technique technique. Read these books from cover to cover and work on your form every day: