I owned a few Honda 350 twins when I was just out of high school. They were good bikes and were affordable. They also broke alot. I suppose that is largely my fault, considering the way I ride. My second one had a broken clutch for the longest time. This was before you had to have the clutch pulled in to start it, so it was possible to ride it without a clutch.
Shifting up was easy, you simply let off the throttle just a bit and shift. No problem. You could do it at any speed under most circumstances.
Downshifting was a bit more difficult, but easily mastered with a little practice. You couldn't really compression brake without a clutch, because it beat up the transmission, but you could downshift. Just bring the RPMs down to just above or right at idle speed, and shift down. It would pop right into gear.
The hardest part to figure out was taking off. Stop signs were easily mastered by simlpy doing a "Califronia Stop", or rolling slowly through the intersection, hoping there weren't any police there. Signals were a different story and often required you to remain stopped for extended periods. I quickly figured out that by shifting into neutral just before I stopped and shutting off the engine, I could wait for the light to turn green, put it in first gear, then hit the start button. It pushed the bike forward while starting it. I guess it was a cross between a compression start (push start) and normal starting with the starter motor.
Since I learned this so early in life, I have been able to apply it successfully to normal riding or extreme riding, and still do it today. When you shift a lot, it takes it's toll on you physically having to pull the lever in all the time, so I usually don't use it when upshifting on extreme rides. This includes other vehicles as well.
The last trip to the desert I was riding a friends quad whose shift lever and clutch lever were not aligned very well for me, making it difficult to shift. After about half way through the first day, I quit using the clutch to upshift almost completely, which greatly increased the fun level and decreased the stress and wear on my old tired hands and arms.
Practice it and you might find you get increased endurance and actually have a better, more effecient ride. I know I do.