There are two thing I think you can do to start with.

The first is to just try greeting people with a smile. Don't worry
about engaging in conversation with them, just practice smiling. Not
everyone you smile at will smile back but that doesn't matter.

The second thing you can try doing is just saying 'Hi" or "Hello" to
people you pass during the day.

You might also want to look at some different conversation questions
you can use to keep conversations going. Take a look at this web site
and maybe print off some of the question sets: http:/
/iteslj.org/questions/

A good trick is to look for open ended questions. Questions such as,
"do you go to this class?" is a closed question. It only invites a
"yes" or "no" On the other hand if you ask someone what they like most
about something, this is an open ended question which will allow them to
talk more and will help to open up the conversation.

Regards

Peter