I would suggest Edelweiss. It's kinda light and not that long. These are also good choices for the start - Katawa Shoujo, Sagara-sanchi no Etsuraku Life, Hinatabokko. Also any of the translated games from Fuguriya if you don't mind yuri.   
Note that all of the games I suggested are just "ok" so you shouldn't expect something amazing, they should serve as a good introduction, though. If you're feeling brave, you could also go for Kanon. Just ignore the "bad art" and you'll probably like it. There are some heavy parts, but other then that it's the usual school slice of life stuff.