A good, no BS way I learned from a Shepard Paine book is to paint the
whites first. Don't sweat keeping it in the lines, you'll fix that in
the end. Next, chose blue (or gray), or brown for the irises, and paint
a stripe from just above the top eyelid to just below the bottom eyelid
that is the thickness of the iris, then paint a thin, black stripe over
that, right down the middle for the pupils. Now take your flesh base
color and bring it in around the eyes. When you're done, you'll have
two perfect eyes with pupils.
There are other, more complicated methods which will yield eye
with more depth, but in 1/35th scale, you don't need to worry so much
about it, however, if you look at the work of some of the masters, even
in 1/35th or 54mm, their irises have light and dark shades as well as a
gleam. Takes practice, patients and a steady hand. The method above
works great and should get you there just fine.
BTW, don't use straight white for the whites. Gray it out, or better
yet, add a touch of your flesh tone to redden it out. That will look
more natural and keep it from looking googly eyed.