Mulching helps prevent water from evaporating from the soil. It also helps protect the soil from crusting and can lower the soil temperature. There are a variety of mulches including compost, straw, composted manure and even aged wood chips.
For the wood chips, check with your extension agent about the type of wood to use and make sure to inquire as to how long ago it was chipped from the live tree. Here's a link to learn more.
You need to know the effect of what you’re mulching with. For example, sawdust can make the soil more acidic. Blueberries love acidic soil (low PH), but other plants might not. Here's a link to learn more about mulch in general. Here's a link to specific kinds of mulch and their effects on the underlying soil.