Assuming you are totally clueless, I suggest you do this systematically.
1. Get a floor plan of your place with dimension. Make a few copies. You need to give this to IDs, contractors, suppliers etc.
2. Go visit show flats, friends' homes, Ikea etc to expose yourself to different styles, concepts, materials, colours etc. Have an idea of what you want e.g. marble, tile or wood floor, what type of built in furniture, electrical.
3. Give the same floor plan and requirements to the different IDs and contractors you meet. This is to allow you to make comparisons.
4. If you are really unsure of what you want to do for your place, or there are budget issues, then I suggest you do the "wet" works first. This means the flooring, plumbing, electrical. Also the kitchen and toilets. Everything else (furniture, electrical appliances, tables, chairs etc) you can buy from Ikea or anywhere, and add them as and when you like.
5. When you sign contract with ID or contractor, make sure the works are itemised and you are able to add/subtract items along the way. You may need to make progress payments along the way but make sure you don't have to pay up almost everything before anything substantial is done.