To start with it's best to concentrate on often used words with regular spellings.
Among the 1st hundred most used words the following all have regular spellings:
a, and, as, at, had, has, an, back, can,
in, is, it, if, did, him, his, big,
get, went,
not, on, from, so, go, no, or, for,
but, must, up, just,
These are a little more complex, but still regular:
that, them, then, with, this, much, little, will, well,
came, made, make, I, like,
our, out, about, over.
The rest are trickier, but as soon as children start writing stories of their own, they want to use some of them:
he, of, the, to, was, first, her, off, they, new,
all, be, been, here, see, are, have, one, said, we, you, by, my, call, before, come, could, do, down, into, look, me, more, now, only, other, right, she, some, their, there, two, when, want, were, what, where, which, who, your, old.