Save my Basil!!!

You can squish them by hand - that's what I tend to do. I have also been known to turn the plant upside down and run a tap lightly over the leaves whilst rubbing the blighters off the leaves. They will tend to congregate on the undersides of the leaves, and probably make the leaves sticky. If you leave them be, they will suck all the life out of the plant. Once it's free of them, perhaps you could pop it outside (assuming it's inside at the moment)? I find I get less of those types of bugs on the outside plants, but they just love my indoor herbs.

If you want to spray, you may try a weak solution of washing up liquid (not such a horrible thought if you use something like Ecover and wash the leaves before you use them. This works on the principle that it's "wetter than water", and will drown them. Apparently...

I mainly squish, often, and keep them at bay. Ick! the first session will be a mammoth one, but there should then be fewer each time.