Details of the cat you should have ready :-

Area lost and when.

Dominant colour - then secondary colours if necessary.
Length of hair - long or short
Any distinguishing features - white paws/white ear/striped tail etc.
Male/female -  neutered/un-neutered
Collar - if so - what colour ?
Age
Name
Is it identichipped ?
Photograph - makes it much easier for people to recognise

LOOK IN
Your house - all rooms, cupboards, washing machine, loft, behind the bath etc.- and anywhere you have been since the last time you saw the cat.
Sheds
Garages
Vehicles
Gardens
Lost & Found section in local Newspapers
Ask neighbours to check their sheds, garages etc.
Empty houses, flats - they may have got in through catflap, open door, windows.

INFORM
Local Veterinary Surgeons
Local School
Any animal concern or charity
Postman and Milkman
Local Newspaper
Local Television
Local Radio

Also, on not a very good note :-
You may not realise that road casualties are usually picked up early in the morning by Swindon Council to avoid possible distress to children who may see them on their way to school.
If you have lost your cat or dog, it is worth sending an email to the Council to see if the animal has been picked up by them.  
Send an email to http://www.swindon.gov.uk/environment/environment-animal-welfare/missingpetsk
or you can email Swindon Cats Protection at LostandFound@swindoncp.co.uk. 
Please donít ring the Council!

ADVERTISE
Put notes through doors in your area
Put leaflets or cards in your local shop windows - with photo if possible
Put a photo of the cat on your gate/in your window saying
 "Have you seen this cat ? "

OFFER REWARD
Say "Large reward". Large is relevant and what is small to you might be a large sum to another person or child.

LASTLY
The earlier you report your cat missing, the more likely that he/she will be found. When your cat does return, DO inform any authorities who have been asked to look for him/her.