If you do sell before you buy, make sure as many things as possible (mortgage etc) are organized beforehand so you can buy quickly
Do your research before you sell. Decide what area you want to buy in, and what sort of property you want to buy
Keep an eye on the property market while you are selling just in case that perfect house comes along. You’ve got time so you might as well use it
Develop relationships with a number of estate agents before you sell, so that you get in there first with all good properties that come up for sale
Get your mortgage pre-approved. This will make you even more attractive to a seller
Try and slow down the selling process, by agreeing a longish period between agreeing an offer and exchanging, and between exchanging and completion. This might give you enough time to buy a new place in the meanwhile