One of the notable things about slide guitar is the use of single string lines. When you slide between each note, you get this beautiful vocal sound with every note connected. Derek Trucks has gotten a lot of mileage playing single string lines. A good way to start is just by using minor pentatonic ideas, then major pentatonic, and then ultimately trying to mix both. Try to challenge yourself by playing an entire section on a single string. I have included a diagram for Minor Pentatonic scale in F below!
If you are interested in learning more licks like this in Open-E and on slide, you can contact me at firstname.lastname@example.org to set up a lesson. If you would like to support my efforts in form of donation my Paypal is email@example.com and my Venmo is Jarred-Garneau