I usually max Q, E, W, and R when you need to.
Her general combo is E + Q *
The more ranks in E increases the charm duration
She has different combos when she gets her ult. Such as:
R + E + Q + W
E + Q + R + W/Ignite
R for gap close + Q for kill + R's to escape
Her ult can go over any wall flash can (I'm pretty sure)
Q gives movement speed when that decays over time, so you can Q but right click left and potentially side step harass.
Personal pref:
Get movement speed. Ahri's 335 ms makes me feel clunky when she gives off the vibe of a high mobile champion. I usually go for aether wisp to build into Ludens Echo and boots to Sorcs (Sorcerers Shoes). With these two items you can achieve 418 ms with 3 points into Fleet of Foot in the Masteries Utility tree.
Playing her in bot games also helps and is not shameful.