Are you matching to existing furniture, carpet, painting etc.? If you have to keep some of your existing furniture this will be the starting block as you cant have a modern chic scheme if you suite is an. Or you may have a family painting/ prize/present you want to live in this room then it cant clash with the finished room.
Choose the big ticket items together and build from there.
Its important to put the whole scheme together at the same time even if you can't buy everything a the one time now you have established where your going and you have a scheme to build on.
Start with the most expensive item.
For example if you are doing a sitting room, the suite will probably be the most expensive item so this might a good place to start. You might chose a fabulous scheme but the suite to go with it is out of your budget. Or you see a lovely suite in your budget but it’s the wrong colour for what you have painted your walls. Remember the tin of paint is the same price, irregardless of the shade inside so pick the paint to match the items in your budget.