E.g. Don't ride the clutch, don't dump the clutch. Make shifts confidently but don't hammer them; let the synchros do their work and feel it slip smoothly into gear.
Along the lines of "feeling" the shift, I have recently been trying to learn to shift without using the clutch. This requires "rev matching" but it's really not rocket science or a bunch of math if you have decent feel for the gears through the shifter. How hard or easy it is to move the shifter into and out of gear tells you how well in sync you are. This is something that I wish I had learned a long time ago, so OP, this might help you.
Start driving and get into, say, 3rd gear. Now (with the clutch all the way out and your foot on the gas, keeping at a constant speed) try to pull the shifter out of gear, gently. It will resist pretty hard, and if you manage to pull it out then you will hear a horrible grinding sound. So don't do it, but just feel the resistance and how it wants to stay in gear even when you put a fair amount of force on the shifter.
However, if you do this right when you lift your foot off the gas after accelerating slightly, it will pull out of gear very easily and with no noises. This is because the revs are matched, which essentially means that there is no torque being transmitted through the transmission. The wheels are turning, causing the transmission to spin at a certain speed, and the engine is also turning at that same speed, so the engine is not speeding up or slowing down the transmission, and the transmission is not speeding up or slowing down the engine. Again, a *slight* push on the gas to accelerate slightly and then an immediate foot-off-the-gas at the same time that you pull the lever out of gear and into neutral.
The trick is really to put pressure on the shifter (enough pressure that it would move out of gear if you were pushing in the clutch pedal) before you start this trick. So you are pulling, not hard enough to pop it out of gear *except* when it hits that perfect moment and the same amount of pressure causes it to come out easily. I feel like I am not explaining this correctly. It is wordy but hopefully it gets the point across.
Now shifting into gear without the clutch is a little harder, but it's the same principle. You have to feel it. Say you are shifting into 5th gear without using the clutch, starting in neutral. So you have the shifter over in the correct position, and you are pushing it like it should go into 5th gear (if you were using the clutch) but not very hard. You keep pushing on the shifter with the exact same pressure throughout this procedure. You've got enough pressure on it that you can feel resistance. Then you rev the engine and let the revs drop. At some point along the line, the revs will match perfectly and the shifter will move forward and go into gear. You have not changed the pressure that you're putting on the shifter, but the same moderate amount of pressure is now strong enough to shift into gear when you have the revs matched.
I always thought that there was some mental magic to rev-matching, that truck drivers had all memorized the exact ratios of engine speeds vs. road speeds for each gear, and that their right feet somehow had ridiculous precision that would allow them to rev the engine to exactly 2650 RPM to get the perfect match. But it's actually based on feel, and it's really not that hard; it's just pulling or pushing on the shifter, and feeling the transmission resist until suddenly it doesn't.
