My property is damp and I am on a limited budget what shall I tackle first?
It is always tempting to put your efforts into working on the areas where you can see the results of damp issues i.e. the internal walls, plasters and finishes. Damp issues, in the main, will be due to the ingress of moisture (mostly from rainwater) from the outside of the property. Therefore tackling external issues such as repairing failed pointing mortar, removing and replacing cracked cement mortars and renders and sorting rainwater goods and drainage is an essential first step.
Failure to address external issues (the root of the problem) can result in any new interior work failing unnecessarily in the future.
Do all that you can to provide a rain screen appropriate for the building and its location, reduce external ground levels where possible and provide active, free-flowing, drainage away from the base of walls.