Get a sponge. As you'll see I've used a dish sponge, which works fine, but a make up sponge will give you a much more polished finish because of the smaller bubbles. Make sure you have a useable size so cut it down if necessary and dampen it to prevent the nail polish being sucked into the sponge.
Paint on the stripes of colour. I've used three: yellow, orange and then red. You can use between 2 and 4 colours, go for more colours the longer your nails are. Bare in mind the whole area of paint on your sponge needs to be just bigger than the size of your nail, so the stripes only need to be about as big as the nail polish brush.
Dab the sponge on to your nail. Try and make the gradient as smooth as possible, so you can move the sponge up and down by a few millimetres to blend the colours together, but not so far that it makes the whole thing the same colour.
Allow the first coat to dry and repeat step 3. You will have to reapply the stripes of colour to your sponge.
Step 4 (optional)
Draw on your palm tree on the ring finger. I did this free hand b drawing the trunk first about 5 lines evenly spaced emanating from the trunk then lots of lines perpendicular to those lines representing the leaves.
Allow to dry and add a top coat