I find the dragons really tough how do you kill them when it's just you I am focusing on spells like fire and shock and i have a week frost spell as well but i really want to give these dragons real smack down. How do to deal with these things?

You need to level up a bunch before they go down easy. But after that it's basically just "Throw [censored] at it until it dies."

Fire dragons have something like a 25% weakness to frost.

Vice versa for frost breathing dragons.

Source: http://www.uesp.net/wiki/Skyrim:Dragon