Learn the location of and
feel of passing through the gears. First learn to
shift the gears without the car running (pushing
the clutch in each time). Then, from the passenger
seat, try it with someone else driving the car and
operating the clutch. Be sure to place the stick
all the way into gear--until it won't go any
more--but don't force it. If you stop halfway, you
will hear an incredibly unpleasant grinding sound
which means your car is not in gear.
Eventually, you will know
when to shift by feel, but early on you'll have to
act deliberately. Even if you've never been in a
car before, you can tell when a car is in the
appropriate gear: the car's not making a coughing
and chugging sound (gear too high) but it's not
making a high-revving sound either (gear too low).
If you have a tachometer, shift around "3" (3000
rpm) on each gear or every 15 miles per hour (1st
gear 1-15, 2nd 15-30, 3rd 30-45, etc.). This is
only a general rule, of course, and higher powered
autos will deviate from this. Shift before you hear
that loud revving sound.