Hello, Idontknow.
There are many ways to improve someone's combat abilities. Since you want it summarized, I won't be describing how, but if you have any questions abou a topic in particular, feel free to ask on comment
1) Level up, better skills and magic level
How your level and skills count on your damage
2) Choosing Better/ Right Equipment (both offensive and defensive)
How damage and defense works (same link as before)
3) Imbuing Equipment
Here
4) Upgrading Equipment Through Exaltation Forge
Here
5) Charms
Need the bestiary though
6) Prey system
Can use both offensive and defensive
7) Temporary buff spells like berserk, sharpshooter and party spells
Individual (note not all the spells of this link are buff spells, but all buff spells I can remember are on that link), Party
8) Skill-up potions (berserk, mastermind and bullseye)
Potions (beware of the nerfs on your defense)
9) Special potions
Tibiadrome
810) Special foods
Hot cuisine
There also are some mechanics to cripple a special monster, like The Welter or Shlorg, so I won't put here. If anyone have another useful method, please comment so I may add here