There are a lot of "little" bonuses you can get in game from leveling different skills.
Alchemy gives a small boost to Power every few levels. Psychology gives extra bonus levels of Mentalism. There are a lot of skills it's good to get 20-30 levels in just for the passive bonuses and unlocks.
Make sure you always have food buffs, and a snack buff if you can. Buy and use consumables like armor kits and first aid kits. "Good" kits that you buy from Marna are perfectly fine at higher levels, as long as you play conservatively. This will help you keep costs down.
Someone else mentioned it too but use your Basic Attacks. Combat refreshes are really important now. The basic attacks have a blue outline when they give a refresh. I make sure to click one whenever it's blue. It gives back health/armor/power.
Have you found and befriended your special skill trainers? Archery has at least 3 in Serbule and there's others in later zones. I know Mentalism has at least one in Serbule that has the good damage-dealing attacks for Mentalism (electricity-based attacks as a hint).
Pick up armor crafting. That will make a *huge* difference. Cloth armor takes a lot longer to level than leather armor so if you're in hurry (as in wanting to catch up) learn to make leather armor.
Not sure if this is a bug or feature, but the cold weather leather armor recipes are "easier" to get (you need less money up front) and you can wear the armor anywhere (even the desert). So it's perfectly reasonable to learn to leatherwork and then head to Kur and buy the cold weather recipes there.
As you're leveling you can skip the various "max enchanted" recipes to save money.
+1 speed bonuses are good. I didn't realize that when I started. Two items with a +1 bonus let you run visibily faster. Also Battle Chemistry. It's great.
Groups help but I solo a lot because it's hard for me to find people and I can get through a lot of content by being patient and picking mobs off one at a time.
Instead of attacking mobs while they're near their buddies at range, walk forward slowly until *one* mob spots you and starts running toward you. Then back up to a safe area and kill that mob. Learn to the judge the distance where mobs shout for help (and pull other mobs) and pull them further than that. The shout shows as a bang (!) above their head.
Also, consider picking up a skill with a pet (necromancy, animal handling, or battle chemistry). Pets help a bit. Animal Handling and Battle Chem are both cash sinks. Necromancy is pretty cheap until you hit 50.
Do you also have good mentalism gear with bonuses for your attacks? For random generated gear, make sure at least half your mods apply to the skills you're using. If not, switch some of your skills around until you get better gear.