A lovely house to me has lots of personality. So YES to decoration like stuff from your travels, big candlesticks, books, cool things your children have made, and lots of art on the walls (doesn't need to cost a fortune, lots of websites let you download art and show you how to do gallery walls). But NO to clutter, so good storage a must.
Also, a clean neutral base palette (e.g. pale grey walls, dark grey sofa, wooden furniture, for example) with lovely splashes of colour coming from your smaller pieces e.g. cushions, throws, ornaments, lamps - but not all 'matching' just complementing each other (pink/green or turqouise/yellow for example).
Plus lots of interesting different textures working together - i.e. leather chair, velvet sofa, sheepskin cushion, wool throw, metal pendant light, glass lamp, wooden coffee table etc. Lots of 'foliage' really helps this - ALL the nice houses on instagram/pinterst have indoor plants galore and often a vase of fresh flowers too.