Some printers, especially the older ones, sometimes have a really hard time feeding paper from the paper tray reliably. It can be rather annoying because you have to sit there and baby the printer while it works. The most common cause for this are old, hardened pickup rollers at the paper tray. Your first step is to clean the rollers with a cottom swab and rubbing alcohol. If that does not help, try taking some fine sandpaper and lightly sanding the rollers in order to remove the tough, oxidized outer layer from the rubber of the roller. If none of this does the trick, you might need to replace the rollers.