All gatherings requiring an invitation have a theme, even if you think they don't. "Let's have Thanksgiving at my place" is a theme. "Who has the biggest TV to watch the Olympics?" is a theme. "I'm bored; let's order a pizza" is a theme.
Once you have decided why you want to invite people into your home and what kind of event you are having, the party planning can proceed from there. The type of event will determine the food, activities, time of day, day of week, decorations, and guest list.
It's great to say you want to have people over, but what do you intend to do with them when they arrive? For a party to be considered successful, you need to plan at least that far ahead.