Bizarre or unusual images are easier to remember. If their prominent feature does not directly fit their name, find a substitute word in their name and imagine it interacting with their prominent feature. These techniques are abstract and take practice. Just trying will focus your attention and improve your memory. If introducing them to another person, say the name you do know and hope the person will volunteer their own name.
Some people use the alphabet effectively to cue themselves.
Decide not to be embarrassed. Everyone has the same problem. Repeat the name. Note the person's outstanding feature. Find substitute words in the name or make a simple association.