Practice packing, unpacking, repacking. Practice, practice, practice. I didn’t and things didn’t fit well in my pack coming back and it was super uncomfortable and painful coming back the next day.
Compression sacks are you friend. I use a 10L for my sleeping bag and 5L for my clothes.
Layers are important. Temperature changes a lot in the mountains.
A backpacking pillow is a good investment.
Don’t make your pack top heavy. My shoulders hurt so bad coming back down because I made my pack way too top heavy.
Bring a lighter even if your camp stove has a self ignite. You never know if it might decide to stop working.
Don’t forget to drink water. It can be colder and you’re focusing on putting one foot in front of the other and not necessarily paying attention to hydrating. Not drinking enough water leads to feeling bad later on.
Have easily accessible snacks.
Have sunscreen and chapstick with SPF. Being in the mountains means higher elevation and closer to the sun. My lips got so sunburned and it was terrible.
If you’re bringing a camera don’t hike with it around your neck. It gets real annoying and heavy real fast.
Bonus: its really fun and totally worth it!!! Now go hit up REI and get out there!