If you have a particular location in mind, the dominant colour might be a consideration. This is especially the case, where the rug is not intended as the main decoration. Furniture seems more of a consideration than the colour of the floor in many cases. Remember, one of the aspects widely prized in a rug is the way unlikely sets of colours have been put together with pleasing effect.
If it's pastel colours which you seek, the rugs from Milas would be a good place to start.
For the floor, wool rugs are best, but a thick Turkish Hereke silk rug feels great in bare feet as you get out of bed. Turkish silk carpets above 10 x 10 knots per centimeter is not so well suited to floors where it will be walked upon. These fine rugs are better suited for hanging on the wall or placed on a table. Silk especially in stair wells with good artificial light - because silk rugs look so completely different depending whether they are viewed from down or up the pile, guests will often comment that the rug appears to have been changed while they were up stairs.
For reception areas and lobbies, go for a big carpet. If your finances and import restrictions allow, central Anatolian carpets are a good place to start. Small rugs just don't work in this function.
If you are looking to buy something for the home, the dimensions of the rug might be a consideration - but not necessarily. In Turkey we've often seen that large rooms contain a selection of small rugs rather than one large carpet. There are several advantages to this: its much easier to clean a small rug in the event of a spillage; if the rug is damages irreparably, the loss is probably less than for a large carpet; they're much more versatile - they give you a way of decorating one part of a room or setting off a particular piece of furniture without necessarily having to consider all the other pieces in the same room. Small rugs can be used is many more rooms than a large carpet.
If you're planning to use a rug under a cherished item of furniture, get a rug that is large enough to frame it generously but not so large that it doesn't fit the area available for the purpose - encroaching on the space of another item.