Problem: my cellphone, a Samsung Galaxy Note, had sheer plastic curved sides that were hard to grip properly. I kept worrying that it would slip out of my hand and smash on the ground. (I tried a silicone case, but it was too bulky and made the phone's back too grippy to easily take out of my pocket.)
Solution: I only hold the phone by two points: the sides at the middle. If these had grip, I wouldn't risk dropping my phone and I'd avoid the bulk of a full case.
Step 1: Buy Non-slip Strips
Non-slip rubber strips can be purchased from hardware stores. I got mine from a dollar store, as you can see by the price sticker.
These ones are 18mm x 300mm in size (0.7in x 11.8in).
These are high-tack rubber grip on one side and have an adhesive backing on the other. They look like nail files/emery boards in this photo, but they're not.
Step 2: Cut a Small Working Section
Here, I cut off a small section to work with. This piece will make BOTH my grip pads. It measures 6mm x 40mm (0.2in x 1.6in).
Step 3: Trim and Finish the Pads
Here I cut the working section [top] in half lengthwise, making two 3mm x 40mm (0.1in x 1.6in) pads [middle].
I then trim all the corners with a box cutter knife [bottom] so that the sharpe edges don't poke my fingers when the pads are attached to the phone.
Step 4: On Phone: Side View
Here you can see the grip pad when applied to the phone's side.
(The stand is a metal bookend that's been bent and covered with light foam padding. I have another Instructable that was featured in Lifehacker that was similar.)
Step 5: On Phone: Three-quarter View
Here's the pad viewed from another angle.
I've increased the contrast in these photos so you can really see it; in normal lighting conditions it blends pretty well with the phone.