Where do I position the tempo relative to the sheet music?

I remember reading somewhere that It goes above the time signature but my memory is distorted.
Yes. Obviously if there's a key signature with lots of accidentals, then the time signature is going to be pushed forward a little. In which case the tempo marking will go above the key signature.

Obviously in Cmaj or Am, yes, it'll just go above the time signature.
The left edge of the tempo indication should line up with the left edge of the time signature. If there's no time signature, then the left edge lines up with the left edge of the first musical symbol (either a note head/stem or an accidental) of the bar.
Thanks guys! Just needed to be reassured by you music gurus.