When it comes to getting the hang of alternate picking, two fundamental questions frequently come up with newer players. The answers, such as they are, may surprise you.
How Should You Hold Your Pick?
When building or improving any technique, and this is certainly true of alternate picking, efficiency and control should be your main goals. But you also have to take into consideration intangibles such as comfort and feel. As long as a motion or position isn’t inefficient or causing any discomfort, it’s worth trying out.
So the short answer is “whatever works”, but you do want to make sure that the way you hold your pick doesn’t create an unnecessary “ceiling”, a point at which further improvement is difficult or impossible.
Ideally, the pick should be gripped with the thumb and index finger, though some players will include the middle finger in tandem with the index as well. The thumb (on top of the pick) should run parallel to the strings, and the index finger (on the bottom of the pick) should be directed perpendicular to the string. The other three fingers can be curled into a loose fist, or splayed out, you can find plenty of examples of each among famous players. Again, the key is whatever’s comfortable, so long as it doesn’t affect your control and efficiency.
Keep your wrist and forearm loose; your grip on the pick should be just enough to not lose control of it or let it slip. Experiment with single-note playing as well as strumming chords across all six strings.
What Type of Pick Should You Use?
This will probably take as much experimentation and practice, if not more, than observing how to hold the pick. Most picks are made of plastic, and some have cork for easier gripping. Some players use metal picks, which are great for artificial harmonics. Players such as Brian May and Billy Gibbons famously use coins (English sixpence and Mexican peso, respectively), which again make artificial harmonics very easy, and have a built-in grip from whatever is embossed on the faces of the coin.
Aside from material, a huge consideration for what pick to use is thickness. A very thin (less than .50mm) will give you less resistance as it meets the string, thus greater speed and flexibility. But you may have to compensate more to strum full chords or get a full dynamic range (such as artificial harmonics or palm muting). Conversely, thicker picks (over 1.00 mm) will give you more control in accurately targeting notes, and getting full strums and dynamics. But you also have to train your wrist for the greater resistance from a thicker pick.
Try at least one of each along the way, until you find what works best for you. I used coins for several years early on, but most of them produce a good deal of metal dust that clings to your fingers. Thin picks give you more freedom and flexibility, but you have to work more at dynamic control. Thicker picks will dial in your wrist and give you more dynamic control, but you have to work at it.
I ended up somewhere in the middle, as I suspect most players do, and I’ve used Dunlop Tortex green .88mm picks for about 20 years or so. Once you find something that works well for you, you’ll probably stick with it for good, but definitely try a few different materials and thicknesses before settling on one particular type. Think about the style(s) of music you play, and what works best for that.
So many of these basic areas of playing boil down to a matter of personal preference, but it’s important to try a few different options before settling on one.