With downshifting, especially as new as you are, it's important to work on smoothness. Roll off the throttle, squeeze in the clutch, tap your toe to select the next lower gear, and then (here's the important part) eeeeeeee-ease out the clutch, get back on the throttle. Most newbies who aren't good at rev matching yet, let out the clutch too quickly. You don't have to take all day to ease out the clutch, just don't let it spring out of its own accord either; a nice gradual release is all it takes.
Also, pay attention to your upshift points/speeds. If you go from say 2nd to 3rd at 30mph, then your downshifts should happen around the same speed. Provided you're not lugging or over-revving the engine to shift, the bike should shift smoothly up/down without any lurching. If you feel lurching, pull the clutch back in a smidge and then re-release slower.
The secret is learning the friction zone. Practice practice practice.