This is probably the number one weak point for most intermediate players. Remarkably few self taught intermediate guitarists have even heard of the alternate picking!
Alternate picking uses a down then a up picking motion alternately regardless of the note that comes next. this makes it much more efficient than just using down or up picks only and also great for any riff or lead line playing fast notes on one string, such as Thunderstruck by AC/DC.
The video references some stretching and warm up exercises, which are in this lesson from the Practice section of this course.
Interactive TAB
The following exercise uses 8th notes which we have to count to a rhythm of 1 & 2 & 3 & 4 & per bar.