Based on our experience, you need at least:
1. Copy of passport
2. Police check (note this is not a CRB check)
3. Copy of highest educational certificate (both you & spouse)
4. Copy of marriage certificate (if you have spouse)
5. Copy of children's birth certificates (if you have kids)
No 2,3,4 and 5 needs to be legalised by FCO and signed by Qatar embassy in UK.

FCO - Foreign & Commonwealth Office
(if you do a search for 'Foreign & Commonwealth Office legalisation', you should find the necessary form online).
Qatar embassy is located in Mayfair/Park Lane area, London (I think South Audley St).