The more I do this job, the more I realize there are a few rules that should never be broken when designing your space!
1) Always pick your fabrics before you choose your paint color! There are only limited colors and patterns in fabrics, but paint can be made in any shade!
2) Always plan your space before purchasing the largest piece of furniture! You can always go back and buy that piece after you've measured your space, but you can't always take it back when it doesn't quite fit! AND... you have to think about how the other furnishings in your room will work with that 10 foot long sectional!
3) Always know what style you are before you purchase! If you purchase something because it looks great in the showroom and it's not at all the style you are or want to be, then you are stuck with a random piece, or changing the style of the whole room to accommodate that one object!
4) Always use scale and proportion in every piece you buy! There is nothing wrong with having a huge wall unit, or a large sofa, as long as everything in the room follows the same scale... but having one large piece and then lots of little pieces just looks odd.
5) Always decide on your budget for the room before you start AND stick to it! Most people think of a budget as the starting point, but it needs to be the ending point. If you have a budget of $5000 for the room, you can't pull it off if you spend $2500 on that gorgeous sofa and you don't have tables, other seating, window treatments, accessories, etc... Planning is key!
6) Always get the advice or collaboration of a professional when you just aren't sure what you want or where to start! Most furniture stores offer free design advice when you purchase your furniture through them. You don't have to take their advice and you don't have to purchase more just because they suggest it, but it is amazing how much better the space can look with just a few tips from a professional! And you don't lose creative control, sometimes it just helps to have someone to keep you on track!
7) Always complete the room before you purchase the "extras"! That means, when you are doing your space, do the finishes first, i.e. walls, flooring, lighting, draperies... If you purchase that great sofa and tables and beautiful lamps and art, but you still have the ugly light that you don't like, then the room isn't going to be "done". You can always purchase the accessories, art, throw pillows later on, get that light or put down that carpet, then you will feel better in the space.
8) Always buy big ticket items first, then get the accessories, you can also save a lot of money on those things because they don't have to be functional, and you can change them easily for a new look, so spending a lot of money on small things can be a waste!
I hope you haven't already started and made these mistakes! And, if you are getting ready to start a big project, or small one... I'd be happy to give some tips and pointers on how to make your designing go smoothly!
Enjoy!