I also use the nails as a guide. If they need clipping its best to do that first and then I trim the hair back from about half way down the nail. For the hair between the nails you can hold the foot from underneath (by gently pushing a finger between a pad) so that is splays slightly and then trim the hair to the same length as the rest.
You will also notice that on the pet trim I take more away at the back of the foot, you can still leave the feathering long but by tidying here it won't be dragging in the wet.
Just out of interest this dog was last trimmed 10 weeks ago. His coat doesn't grow especially fast but as you can see from the first pic by the time 10 weeks has passed they are still pretty hairy. Thats why I trim as short as I do..... to make it last a bit. If I didn't they'd be back to looking like Hairy Jeremy in 3 weeks
Pam, I trim vertically around the foot, for the most part anyway :-
but I'm sure you & Jane and anyone else will agree that we are all different in our style of trimming anyway