Use a truncation symbol (the asterisk * is the most common) to look for different word endings.
You do have to be careful with truncation. Sometimes you might get unexpected results.
Use AND to join dissimilar terms. It helps narrow your search.
Use OR to join similar terms. It helps broaden your search.
Use AND and OR together, too.
Note: When inputting your search in one line, the parentheses keep the like terms together. Putting your search in one line makes it a bit easier to copy and paste between databases.
Use quotation marks to search for a phrase (two words or more).