The combat level is affected by player’s combat skills or NPC. Of course, the higher level the more combat skilled or NPC. The combat level is depended on the armor and weapons that an NPC has, natural or equipped.
Training combat in runescape has many ways. We not only give you some useful skills guide to convenient you but offer the cheap RuneScape gold to meet you game need in fast and softest delivery.

Levels 3-20
In low level, you could accept two options:
Kill chickens: Chickens located near the cows in Lumbridge. You should cross the bridge, next to the cows and find chickens to kill. They drop feathers, raw chicken and bones.
Kill cows: It is a wonderful choice in low level. They drop bones and cowhide. Cowhides can be good runescape money for players which can be sold for 100 each or more in the Grand Exchange or to other players.

Levels 20-50
Fight Al Kharid Warriors in Al Kharid, or you can keep killing cows for money as well as combat levels.
When you are stronger you could fight with more powerful monsters and train with Hill Giants in Edgeville Dungeon.

Levels 50-76
You are strong enough to kill Elvarg the Dragon (level 83) and complete Dragon Slayer. When you finished, you'd better to buy RS gold in a suitable amount for the later combat.
Now you can train in Crandor or Karamja Dungeon who would give big bones, and cool stuff like laws, natures, deaths, cosmics, gems etc.

Levels 76 and onwards
It is a hard process to reach this level. You can now train with Lesser Demons which have a combat level of 82, or you can train with Ice Giants. When you’re level 90+, try to kill Ice Giants in Ice Cave, south of Port Sarim. But this monster is very powerful, you must prepare combat strategy and plenty of cheap RS gold to do you favor or you will die soon. rsfirm.com is glad to give you fast RS gold help in any time to satisfy you.
If you win the combat, Ice Giants will drop items pretty similar to what the Moss Giants drop, with some additional items such as Black Kiteshield.