How should I practice to improve?

One thing my Instructor told me that has helped me as well. When you are on the driving range. Hit a ball and then take a step beck. Aim every shot at something, like you are on the course. This has helped me get into a routine for each shot on the course, and my shots are more consistent now.

As far as what you should be working on with the percentages, that's a perfect question for your Instructor, since you have one.

I hate to say it but I NEVER practice putting. Its just boring to me. Fortunately I have a good feel for it and while I could improve, I am happy with my results right now.

Range wise, I like to alternate between long and short clubs so I can get comfortable with the transitions. If you hit wedge, wedge, wedge, 9, 8 etc you will get in a groove with each one but on the course you don't get to do that. So I go something like 8, 5, 9, 4, P, 6, GW, 3W, LW, 5W, SW, D and just hit 3-4 shots per club.

That's not to say that you don't need to focus on one or two clubs sometimes and get them dialed in. I do this with Wedges and Driver a lot and pick a different club each session to spend extra time on.

Finally you need to play some. 9 or 6 holes is perfect. I like to go and hit on the range for 15 minutes and then walk over and play 9 holes, maybe 6 if its late or hot (course has a perfect spot to jump from 3 to 7). Tough on public course I know. This is probably the biggest benefit I get from my club membership.

Of course it all depends on where you are with your game. OP is a 20 so I would say you have plenty to work out on the range. Once you get down to low teens (at least in my experience) there are more improvements to be made on the course itself. Course Mgmt, confidence and just the general progression of a hole from tee to green (carrying that water hazard for example).

I practice about 1 and 1/2 hour every day after work and this is my routine.  Take from it what you will, it has worked for me so far.

Driving Range - About 75 balls (40-50 minutes)

• Order: SW, PW, 7i, 4i, 9i, 6i, 3i, 8i, 5i, 4w, 54degrees, Driver, LW (58degress)
• Method: For the first 5 or so shots, i'll lay down alignment sticks for the path of my club to follow on the takeaway and follow-through. After that, i'll take away the alignment sticks, stand back and pick a target for every shot. 

Chipping - (20 minutes)

• Order: SW, LW, PW, 8i
• Method: I take a hoola-hoop that has about a 3ft radius and i'll place it around a flagstick on the chipping green, and just chip from different areas with the goal in mind to get the ball inside of the hoola-hoop. I try to work with as many slopes as possible and use more realistic spots rather than just place them just outside of the fringe.

Putting (w/ some chipping) - (10-20 minutes)

• Method: I'll start off by hitting about 15 putts from 3feet using alignment sticks as railroad tracks to keep my putter square through the entire stroke. Then i'll do lag putting from 20-40 feet with the goal in mind to two-putt all of them.  Afterwards i'll take 5 balls, my sand-wedge and try to get up and down with all 5 of them, and usually I won't leave until I get all of them up and down.

The most important thing for me is to try to make a game out of every drill.  Maybe make point values or something and try to beat my personal record. Hope this helps!