Welcome, Nate! And congratulations for sticking with training for 6 months. Consistency is one of the big factors in success.
Lift for muscle. Eat for lean. There is no way to lift that will give you "lean muscle". The leanness is a product of a low body fat percentage.
8-12 reps is a range that some people advocate for muscle hypertrophy, but since big isn't one of your goals, it might be better to use somewhat lower reps, which would allow you to lift heavier weights and get stronger. Don't worry, "bulking up" takes a lot of dedicated, focused work. You don't bulk up accidentally! If you are eating for lean, and lifting for strong, you will achieve your goals.
The legs are very important, and deserve as much emphasis, more really, than bicep curls and shoulder presses! Also, try to use mostly compound exercises, those that use more than one joint at a time. It's just more "bang for the buck", more "value for the dollar"!
I like the simplicity of your routine. Keeping the number of exercises down allows you to get more out of each one.
Here are the exercises I'd suggest you include for now:
A squat, or squat variant
Deadlift, or a deadlift variant
A horizontal pressing movement (pushup or bench press)
A vertical pressing movement (shoulder press)
A horizontal pulling movement (some sort of row or pull)
A vertical pulling movement (some form of pullup or pulldown)
Along with that, you can do a few "isolation" or accessory exercises for variety or to emphasize something that you want to emphasize, and a couple of core exersizes. Some possibilities are:
Curls (any of the many types that exist)
Triceps exercises (again, there are many)
Calf raises (actually these are a compound exercise, but they group better with the isolation lifts)
Carry, like a waiter's walk or a farmer's carry
There are thousands of other exercises, but these are pretty basic.
To organize your workouts, I'd suggest a full-body approach. Do one of the big leg exercises first on 2 or the days, and one of the upper body lifts that you'd like to emphasize on the third, each time followed by one of the other upper lifts. Then do 1 or 2 accessory/isolation lifts. It could look like this:
1. Squat, shoulder press, pull-through, curl
2. Deadlift, pull-ups, triceps, planks
3. Bench press, row, calf raise, farmer's carry
Obviously, you can use that basic idea and do many variations.
You don't have to be rigid about the number of sets and reps. You can try different ways to do it. You might start with something like 3 sets of 5 reps. Start light, and add weight from workout to workout until it starts to get heavy. When you feel that you can't add weight and still do all the sets, then just add weight to one of the sets. Next time you can add it to another, and later to the third. Or you can just add a rep or two to one or two sets. When you start to feel like you can handle more volume, you can even add another set. If you feel good on a particular day, push yourself a little harder. If you are having a bad day (i.e. short of sleep) just make a little progress over the last time you did that workout. Try to make some kind of progress each time, but if you are really feeling bad (i.e. sick) and can only do what you did last time, so be it. No harm done. If you keep adding sets and reps, you will eventually find that you are doing many more reps and more sets than when you started. When that happens, just go back to the original number of reps and sets, but this time with a slightly higher weight, and then go on from there.
For the isolation/accessory lifts, just pick a combination of reps and sets, maybe a bit higher reps than your "big" lifts, like maybe 3 sets of 10. Use enough weight to make it seem like a bit of work, but don't bust your guts on those. Just increase them slowly over time. They are not your "money" lifts.
For a college student you may be able to plan certain days to lift, but you may have to be flexible. Just do the three workouts in order. If you have to miss a day, just do the next workout in the rotation on the next day you can lift. There is nothing magical about certain days of the week, or a fixed number of days per week. Most of the time, you should have at least one day off between each lifting day, but if once in a while you want to lift on subsequent days, it won't really hurt anything. If you have limited time on some days, just do the 2 big lifts that day, and forget the accessories. I'm a big fan of flexible.
So lean muscle isn't related to your repetitions? I have always been under the impression that lower repetitions achieved bulkier muscles. I understand that you must have a low percentage of body fat, however, I thought the lower repetitions would still make your muscles larger in actuality. If that is the case, how would you eat for lean?
I appreciate the example routine. I'll make sure to give it a try. Do you have a different exercise that may work the same muscles as the farmer's pull. The gym at my school isn't the largest, and I don't think it would be a great idea to walk around carrying weights.
Thank you for all your help so far.