i never downshift into 1st... if im moving.. i use second..... they say it's save to downshift into 1st if your going < 5mph... but even then i'll still use 2nd... the engine is strong enough that it wont stall if you're easy on the clutch
NEVER downshift into first, if at anytime you should be downshifting into first its when you are rolling at 5 mph and you feel the car about to slow down to a hault, then downshift into first right before the hault to keep going.
what i do is that if im rolling at all (say 5mph-15) ill be in second but i let the clutch out reeeeaaaal smooth and get the proper clutch pedal/gas pedal mix. also if im going like 20+ around a turn or corner ill be in third..
NEVER downshift into first if your moving, you will hurt your clutch
FWIW, the only reason to refrain from downshifting into first is because you will wear out the synchro for first gear very quickly. It is the heaviest gear in the gearbox, and requires the most braking effect to get into gear. When you downshift into first, you are asking the synchro to stop the heaviest gear in the gearbox, so it will wear the most. However, if you understand gearboxes and rpm, it is possible to do this in a way that minimizes the wear. Unfortunately, since you are a noob to manual shifting, I wouldn't recommend it until you develop a greater experience base from which to decide how to use your gearbox.
Yes, I have rebuilt gearboxes and I can show you pictures of the results of downshifting into first when you don't do it right.