While it's absolutely true that tastes change and are developed and finessed over time, your innner roots will always come through in what is pleasing.
Don't be afraid to paint a color you love. Purple makes your heart sing? Use it on things you see daily; a pair of large shams on the bed, a bold piece of art in the entry, the curio in your dining room. 
Mix up styles you love. It's fresh and fun to add casual distressed wood dining chairs to your elegant upholstered armchairs around the table. A modern bookshelf can look fabulous in a traditional home. Mixing styles gives you opportunities to incorporate interesting and fun elements to create a personal space. 
White is always right. Boring white? No way! It's often the best backdrop for any room. Not only is it classic and attractive, it allows so much flexibility in design and decor over the long term.
Bigger is better. Don't opt for the little matching vases when selecting accessories, larger will work and create a fabulous focal point. Small scale items often lose their impact in a room. Got lots of tiny collections? Group them together! Small furniture actually makes rooms look small. That doesn't mean that ALL of your pieces should be oversized....a bed, a curio, an armoire and even a sofa in a grand scale will work better than many small pieces.
Pair things up. Symmetry is classic and appealing. Get two buffet lamps. Buy a set of fun pillows. Pairs can be identical or 'matched' by color or scale. Hanging paired frames and mirrors might be all you need. 
Less is more. In comfortable homes, things all feel 'right'. The more items in a space, the more cluttered it looks. Each piece you use should have a value. For example, lots of people think that every chair needs a table next to it.....that only clutters a room with legs. Using a great ottoman, trays, buffet tables, and even plant stands, gives exactly the space you need for coffee and teacups without crowding.
Embrace dark, rich colors, contrary to popular opinion, a dark wall color can make a room feel larger. How you position your furniture - not lining the walls - is key.
Who says you need a sofa? In so many client homes - especially those with children - one sofa takes up too much floor space and only ONE child lounges over 2/3 of it. Club chairs, even in mixed styles, make seating flexible, comfortable, and take up less apparent space.
Go ahead and mix metals. Gold and silver are awesome together. A beautiful brass chandelier abdolutely works with silver mirrors. It's all about the proportion and how those colors are balanced together.