You dont need to smile, just dont scowl
Before you go, think of about 5 or 6 topics of conversation you could start.
The weather, do you have any holidays planned? What do you think will happen with Iran over this tanker situation, do you have any kids, how old, are they looking forward to summer holidays, how do you know the host, I like your shirt/shoes/bag where did you get it from.
Get a little piece of paper and write a prompt for each one on it, add any names of people you should remember and when you get to the party tuck the paper somewhere easy to get to.
If you get stuck for conversation, pop to the loo or refill your drink or step out for a breath of fresh air and scan the paper.
Then dont stay talking to one person for too long, be a butterfly as you can have the same conversation with different people.
If walking into the room isnt a problem for you, then I would turn up a little late so that there are lots of people there already, I find that easier than a room with just a couple of people.