Shy people can't directly stare you in the eyes or come talk to you. So they will give subtle signs like staring across the room, looking at you but not maintaining eye contact.
If they get extremely awkward in front of you like giggles irrespective of conversation, or box conversation, it means they are trying to have conversation but are awkward.
Shy people usually stammer or get nervous when talking to the person they like. It may come as surprise but they can't help it, so you should know it as a sign they like you.
Shy people usually can't talk in front of people they like but they are more active when talking online. They will flirt a lot when online which is a sure sign they like you.
Shy people usually get uncomfortable while talking about themselves. It's just they can't do it but they will keep the conversation on by asking you about things.
It is a sign if he is accidentally touching you on the shoulder or on the hand, as it may be a little awkward for them to open up. So consider it a sign.
Shy people surely can't open up about their feelings when around you and are sober but they will open up when drinking.