Pick your color theme. For example pink and green for girls or blue, red and green for boys.
Next, pick your child's bedding and room paint color. This can be done in any order. If you, start with the bedding first, you can easily bring a pillow sham to the store and narrow down your paint choices. To create that "designer look" pick fabrics that coordinate well, like stripes and polka dots or solids and plaids/check/gingham.
Mix and match furniture pieces. This gives you more options in the future should you need to swap out items your child grows, without having to replace all the furniture in the room.
Purchase a small amount of each color that you like to paint a swatch on your child's wall at home. This is money well spent, it's always best to see how the paint color reacts with the lighting in your child's room.
Now here's where the fun begins..accessories! Keep in mind your child's room is a work in progress, ever changing just like your child. Start with the basics and then add those special touches over time.
Do not try match room colors exactly, it's best for colors to coordinate and compliment each other. This gives you major flexibility when shopping for room accessories such as wall art.
Remember to hang wall art, frames and shelves out of a child's reach. And, avoid hanging wall art in direct sun light, excess sunlight can damage many types of artwork.
Now go out there and have some FUN!