Knowing how to spell the 100 most HF words is a very good start.
Half of them have regular spellings (a, and, at, had, has....).
The following (in order of frequency) are trickier:
I, 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.