The best resource for this is
barella's guide.
Essentially, there's a 600 minimum for UK domestic flights and an 800 minimum for all others. Double miles for business, triple miles for first. There are some exceptions (eg SQ) and you need to be careful of discount economy and web fares (50% and 25% mileage respectively) on bmi flights only (but it's thought you can book *A codeshares on bmi metal and avoid this problem).