Personally, I like staying relatively low-level--when I actually do level up, I have a habit of making it past where the level cap is for the boss in question, whereas in this runthrough Seifer was actually a higher level than Squall at Deling City. I was so pleased with that.

But for me, I just used Scan and tried to be very careful about attacking anything--drawing and casting magic with your low-magic-stat party members is usually helpful, and once you get Diablos, he'll be invaluable.

..For my part, I still didn't like to run, so I just took it when I met things I couldn't Card, and still managed to stay under level 20 until about midway through Disc 2, when I stopped bothering so much.