The first and probably the best tip is to get a wolf. If a giant comes after you, send the wolf on it and run away to a safe distance. 3 good defensive skills for giants are Lightning shock, Charged wind and Root. Get them, or at least the first two. Also Earth barrier is a must. Even if you find the invisibility skill, because of people altering their game to see you anyway, get the first level of it, so you can sneak past at areas that are a bit too much.
Grind on mobs that you can two hit by using Ice and Fire bolt always start with ice. You will never have to worry about your mana running out either when using these two nukes. The Ice/Fire bolt combination is fast and it should keep you from getting hit. When the zerkbar is full, do not use it on a giant unless you know you can handle it but rather go after the normal mobs, also you can then also put to use your aoe skills more safely and effectively. It is as good xp wise as going after a giant.
If you are grinding on mobs that does not spawn giants or champions, you can use Life control. We would not recommend it otherwise. Do not bother about mobs that have range skills, since you will always then get hit at least once between your nuking. With cleric sub you can easily take on giants and with bard sub you can safely grind in areas where the mobs are aggro.