You're picking doesn't really suck- I was just getting your attention! However, many people struggle with the transition from strumming all the strings to picking single strings. The first thing to understand is they are very different actions.
Strumming is an arm movement from the elbow, your wrist should be pretty still and close to the guitar.
Picking is a wrist movement. Your wrist should be resting on the guitar above or on the strings.
Key picking points from the video
- How the pick between your thumb and the side of your first finger
- Rest your wrist on the guitar (or the strings themselves if playing thinner string)
- Keep the picking movement small and from the wrist!