Decide what you will be doing with the computer first. Gaming, web surfing, editing, etc. Then choose your monitor based on that. For instance, If you do photo editing, choose an IPS panel monitor with good color accuracy. If your a gamer and value performance over image quality, you might get one designed for gaming. Once you narrow that down, you can pick the video card that will drive your monitor at whatever FPS and quality settings you're shooting for in games, or has the outputs you need for multi monitor and so on. Then you pick a CPU that will have sufficient power without bottle-necking your video card or one that gives the best performance for editing, multitasking, whatever. Then when you have your CPU, you can pick the motherboard that has a compatible socket and the features you want. Ram will depend on what you do with it, but consider 8 GB's minimum. Once you have all these components chosen, you can calculate your system wattage and and what size PSU you need. Tom's has lots of stickies and charts which will help you. When you finally sort out your build, use PCPartPicker to build your system and then you can post it on the forums here for input.
www.pcpartpicker.com