Many people struggle to make new builds look homely and lived in. As the property itself will lack any sense of history or character, you'll need to inject a bit of a sense of personality through your furniture and belongings.
Furnish from the past, present and for the future
If you don't have any family heirlooms (no - your college billy bookcase doesn't count), then try buying pieces which aren't all ultra modern and contemporary in style. You can soften the look with a few older pieces, either faux vintage from somewhere like West Elm who specialise in mid century modern furnishings and homeware, or getting the odd item from eBay or a physical auction house. It will give the impression that the house has always been there, and that you have a history, rather than just feeling like the world started in 2015 when you got the keys.
When you look at homes in magazines or go to stately homes or see character's houses on TV, they will be dressed in this way and your eye will have become accustomed to seeing a variety of belongings in order to look natural. After WWII many people didn't have any possessions left, or never wanted to be attached to anything that could so easily be taken away, so there was a trend to kit out homes entirely in the fashion of the time, so you might think of a super 60s or 70s home (shag carpet and orange flock wallpaper) but I think you'll agree they don't look like homes, more like museum or film sets.
Other options include bold wallpapers on feature walls (accent walls which are darker or smaller, don't just whack something colourful on the chimney breast. Don't think feature wall)