Once you have established your date, order some postcard invites. I use Moo.com for mine, and usually add a nice picture of my jewelry to one side, and the details on the other. Order them in plenty of time though- you want to hand those invites out as soon as you can as people tend to have busy schedules in the colder months.
I think it's good to stick to people you know, and encourage people to bring a friend. In the past I have offered a small discount if they bring someone.
I plan my open house for about 4 hours, generally in the afternoon from 1-5pm. I think you could also do one in the morning like 10-2 - some people are early birds. And an evening show like 4-8 would be a good time too, with different lighting. I have poor lighting in my house so the 1-5 works out perfectly for me.
I hope these tips were helpful for you and that you consider having an event like this too. It's really a good time, you get to chat with people and see their reactions to your designs, and provide them with a comfortable shopping experience. I know they'll keep coming back year after year!