In my basic alternate picking guitar lesson - Alternate Picking - Absolute Basics! - I took you through a series of simple exercises that while perhaps ridiculously simple, were designed to get you on the right foot, or right and left hand, in terms of developing speed, accuracy, and synchronization. I also purposefully designed those basic exercises to reinforce muscle memory, agility and dexterity in your fingers, so that in the end you are getting a two-for-one deal. I believe that is always a good approach to practicing - reinforce different concepts at the same time.
You can think of the previous guitar lesson as a stepping stone. By training your fingers pairwise to have dexterity, speed, and accuracy, you are now ready for the next step, which is mastering three note patterns. If you look closely at any guitar solo or riff, you will see that you can break almost anything down into three note fingerings plus position shifts. I'll cover position shifting later, but having mastery of three note patterns, as well as position shifting, you will then be armed to effortlessly play almost anything that comes your way, as well as anything that you dream up. It is all about building blocks.
As I mentioned in the previous guitar lesson, when practicing the alternate picking exercises you should always focus on precision and timing, playing to a metronome at a comfortable tempo. Make sure you are not losing synchronization between your right and left hands. With three notes in the mix, there is now more room for error, but if you progressed through Alternate Picking - Absolute Basics! then your fingers should already be well conditioned to handle the exercises in this guitar lesson.
Likewise with the previous guitar lesson, note that in the tab for each exercise I indicate several fingerings. Practicing all fingerings has the added benefit of preparing your fingers for four note patterns. You will appreciate this fact when we get to four note patterns - trust me!