Bikes are complicated machines. I didn't realize that until I started mountain biking 6 years ago! Without getting an entire new bike, here is a list of simple bike upgrades that can make your feel like an entire new bike!
Bike Fit and Saddle
Did you know that your cockpit, handlebars, and just about everything on there is adjustable?? Pay one of Local Bike Shops a quick visit and ask them to help you. Brake levers, saddles, handlebar width, and more are adjustable and can make a HUGE difference.
Pedals and Shoes
Did you know the pedals that come with your bike are test pedals?! And aren't meant to be ridden on trails? Upgrade to mountain bike specific pedals that have pins in them. These pins will help you keep your feet on the pedals and in the place you want your feet to be. The pedals will also survive those pesky rock hits.
Good Pedals start around $50. Popular pedals include Race Face Chesters. Personally, I have HTs on my bikes and love them. They are pricey, but I've had them for YEARS. If you upgrade pedals, consider upgrading your shoes as well; 5.10s and RaceFace are popular brands. Hiking shoes/boots can also work, but the pedals may destroy them.
There are SO MANY different tires to choose from! Here in COS, we have a lot of loose gravel on hard packed dirt and thick kitty litter. Consider a tire with a lot of knobs for more grip, especially on the sides. You'll be happy with how confidence inspiring knobby tires are in loose corners; it truly has made a big difference in my riding. Again, I recommend asking a Local Bike Shop to see what folks run around here, and then it's easy to ask them to install your (hopefully) tubeless tires! There's a good chance your front and rear tires will be different as they serve different purposes. Finally, should you go tubeless?! Probably, everyone's doing it. Seriously though, the benefits of tubeless are endless: more traction and the sealant fills in small holes/tears caused by cactus or goat heads. Sealant needs to be refilled every few months.
Finally, these are just my personal suggestions; I encourage you to find what works for you. Upgrading bike parts can be really fun! Consider going to any of the Local Bike Shops for assistance. Criterium and Ted's are WMBA Sponsors and excellent resources!