I never saw a big problem with buffing my mage throughout her journey to level 60. Each of my buffs (Arcane Intellect and one of the two shields) were both 30 minutes long, and there was no real issue to remember to keep those buffs on. As I started leveling my priest, the 10-minute (max) Inner Fire, seemed to give me problems. Not to mention the Shadow Protection spell had the same problem for me. So, a friend of mine found a mod that would buff you, if needed, pretty much anytime you did anything. Whether you were turning or walking or running in circles, if you needed a buff, the mod was there. (Darned if I can't remember the name of that mod. Autobuff?)
Another mod from back in the day was Decursive. This one didn't have a pretty interface like most other mods I've used, but you would set up a macro to trigger it, and it worked great. Basically, any curse, poison, magic effect, etc. (based on your race) in your party or raid would be detected and moved when you clicked this magical button. It was great.
Then came the dreaded day for a lot of guilds when patch 1.10 came out. Blizzard no longer allowed you to hook procedures off of movements (that ruined Autobuff), nor did they allow you to cast a spell without first determining which target you would cast it at (bye-bye Decursive). I know this really devastated a lot of raiding guilds, but I can certainly understand Blizzard's point of view. They actually wanted us to think, and not mindlessly click a button until it said everything was clear.
I don't know if there's been any development directly on those mods, but the same friend showed me a replacement a long time ago. SmartBuff and SmartDebuff can be found on curse here. There's all the settings for all the classes. You can pretty much decide how and when you want to buff members of your group. It's not as easy as moving to cast, but it's still pretty darn simple. Once SmartBuff is all set up, you only need to scroll your mouse wheel and it will buff everyone in your group.
One of the great things about SmartBuff is that it takes some of the checking off your shoulders. You don't even have to check if Joe-Priest has Intellect on him if you absentmindedly zoom in and out like I do. If you're in a raid, you can click on check boxes to determine which party (or parties) you'll be responsible for buffing. And if those members aren't in your party, you would normally have to figure out if they have the buff (by either selecting them or looking for some small icon), then targeting them, and then casting the spell. Bah! Sounds like a lot of work. Just let SmartBuff take care of it for you.
SmartDebuff isn't quite as simple, but still is a huge time saver for me. A box similar to the one shown here is available to you. If you're solo-ing, it will have only your name in the box. When you're in a group, more names will come in. Personally, I have mine broken up by classes, but I believe there's a few options here. And hard to tell how fro this picture, but either a large "R" or "L" will pop up on the names. (I'm assuming it's the red ones how this picture has it set up.) As a mage, you only have to ever "L"-click (left click) the cursed members. But if you're a class that can get rid of multiple ailments, you'll either have to "R"-click (right click) or "L"-click the persons name. It's that simple. You just have to pay attention to the box. :)