Write i before e
Except after C
Or when sounded like ay
As in neighbour and weigh.
which is to say, you should generally write ie except under TWO conditions.
1. when the two letters follow c
2. when the two letters sound like ay (as in day)
Some ie words:
believe, belief, chief, field, grief, relief, yield, siege, niece, friend
Some ei words:
ceiling, conceit, deceive, deceit, receive, receipt, neighbour, eight, weigh, weight, vein, skein