Ahhh. The art and skill of Magery.
There is a lot of ways you can efficiently train this skill...as well as others at the same time...I'll list the method(s) and you can look into the gp/xp and xp/hr rates; Here are some ideas;
If you just want MAGIC XP ONLY;
Alching (of course) - Boring, but can be profitable
MTA (Mage training arena) - not the quickest, but yields a nice sum of GP
Basic Magic combat training - through spells via Slayer? Dungeoneering? Gano's (for gp)? etc. which ever you prefer
Efficiency route(s)
Other methods that yield xp in other skills;
Alching while fishing, mining, woodcutting - Doesn't intterupt current skill being trained. Which means in the long run your saving yourself a lot of game ticks as well as time in-game training...ahhh, efficient c:
Superheating Gold Bars via LRC - again, no loss of game ticks, and by the time you hit 99 mining you will have about 93-95ish smithing, well over 99 magic.
If it is in your desire to raise your summoning level or even go for 99, it would be profficient to burst/barrage rock lobsters for the high charm drop rates and awesome magic xp / hour...Reqs include; 86-91 magery, ancient magiks unlocked.
these are just a few of the countless many many many ways of training magic. methods I posted include time efficiency, low and high gp / xp rates,
low and high xp / hr rates, etc...all depends on how much money you want to spend/gain, and how much xp / hr your willing to train at...its all up to you bud c: hope this helped!