Try experimenting with mixing different series. I like to match furniture on theme and colour, using complete sets doesn't worry me. If possible try customising furniture too, the cabana series looks awesome 'colorful'. Beyond that I try to layout my house so that it's somewhere I'd be willing to live. Meaning each room has a purpose. I have a living room, a gaming room, a kitchen, a bathroom, a bedroom, and a basement filled with items matching the mad scientist theme.