How do I shop for a good tire?
Unfortunately the answer is the same as how you judge the quality of any product. Experience with the product, brand reputation, price (higher correlates somewhat with better performance) and searching for and reading reviews.

With respect to your current tires, they are probably not worn out. Not even cheap tires wear out after only 750kms. Road tires have a very shallow 'tread' pattern that is really just cosmetic - bike tires are narrow enough to displace water easily and do not need tread to grip tarmac or concrete surface. See How do I know when to replace my tires?. 

Also, you should know that higher inflation pressure does not necessarily mean lower rolling resistance on rough surfaces. See this answer and this GCN video.