I generally only need to do this once for each project, which means I don’t do it often enough to remember. Log in to the MySQL server as root, then:
create database newdb;
grant all on newdb.* to 'newuser'@'localhost' identified by 'newuser';
set password for 'newuser'@'localhost' = password('newpass');
And you’re ready to go!
Replace newdb, newuser and newpass with whatever you like.