To stand any chance of the gain on the sale of a residential property being wholly or partly exempt from tax, one of the requirements is that you can show it was used as your only or main residence.
There are a growing number of tax tribunal cases on this issue, where whether or not a property has been used as s residence is a question of fact with evidence being vital to obtain. That really is the basic message as a lack of evidence will be fatal where you lived in a property for only a short time.
As to what evidence is needed, that all depends on the circumstances. Forward planning is vital, as is being able to show that there was an intention (albeit not necessarily realised) to live in the property with some degree of permanence.