As guitarists, we want to utilize different picking techniques like sweep picking and alternate picking. Alternate picking is the combination of downstrokes and upstrokes and is an essential technique for all guitarists, regardless of their genre. Alternate picking is faster, more controlled and easier than relentlessly down-picking a guitar string. By only using downstrokes we’re using twice as much energy to get half as much speed. Not all guitarists are as obsessed with fast playing as others, but speed is something the vast majority of guitarists will employ at least some of the time.
The following is an alternate picking exercise that is inspired by J.S. Bach's Sonata No. 1 in G minor - BWV1001 - Presto for violin. I found the fourth measure of the Sonata to be difficult, so I created the exercise to help me execute it within the piece. It's played by using only one note per string on guitar. What makes it difficult is that you are alternate picking while crossing strings, meaning that as you move your pick down to the next string you pick upward.
First, find the notes, start off slowly, and eventually play it with a metronome at 50 bpm (dotted quarter note or one measure's worth). Make sure to alternate pick every note no matter how awkward it may seem. This will help your picking technique immensely over time. Be sure to play it slowly and without any "clunks". Be persistent and you'll get it! Good luck, enjoy, and happy picking.