From what I have read, while in combat, the more you use a specific spell the more you will level that spell from novice upwards.

Although currently i'm level 50 destruction, some spells i have used more than other in combat are still listed as novice? and I got a newly acquired fire spell and it's listed as adept.

I am confucious

Spells do not level. Skills level. The ranking that a spell lists simply lets you know which perk is relevant to it and around what skill level you can start buying it.

Thanks.

Now this being the case, would mages generally just be using their higher rated damage spells?

Depends on the purpose. Before you have the high-end perks, the advanced spells will drain your magicka very quickly. In addition different spells are ideal in different situations, such as when dealing with multiple enemies versus a single one.