Just start small. Real small. Remember that raiding the center of a town is generally for the mid-game or more advanced players, although if you do a night raid it can simplify matters somewhat-- or not as the case may be.
Prioritize what you’re looking for and from that, prioritize what to raid. Houses on the outskirts are a nice way to start invading a town, make sure to clear the street any nearby zombies so they can’t interrupt. Once you have a safe place to return to and a safe place to sleep everything else pretty much falls into place.
[ol][li]
Firstly: Clothes and storage. Backpacks, army pants, shorts, jackets etc.[/li]
[li]Secondly, tools, books etc.[/li][/ol]
As to what stores to raid, military surpluses or sports goods stores are generally my first choice, followed swiftly by libraries. After that, a grocery/supermarket for a trolley cart, food and drink… hardware stores for nails and a nailgun… the list is endless.