No two monitors display colours in exactly the same way, and yet the only way we can view an image before we print it is on screen. How can we tell what the print is going to look like? Start by calibrating your screen.
If you're serious about colour management, we strongly recommend that you buy a colorimeter and use it at least monthly (or whenever you think someone has fiddled with the monitor controls!)
Colour variation can be caused by something as simple as altering the controls, but in fact all devices display colour slightly differently. The whole point of colour management, calibration and ICC profiles is to adjust for those differences so that in the real world the colour looks the same wherever and however it is viewed.
A necessary step is to calibrate the monitors at each location in your workflow (eg. your laptop, your studio desktop and our lab) to the standard defined by the International Colour Consortium (ICC) by means of an ICC colour profile. This is a "map" defining the colour that is to be displayed when the monitor receives a particular set of RGB values. Each monitor requires its own ICC profile.We calibrate our own monitors regularly, and you should do the same.
Note that while most profiles just describe the behaviour of a device, a monitor profile also changes the way the monitor displays colour.
Software-based calibrators that work based on your own visual perception are not reliable. A measuring device such as a colorimeter will measure the colours displayed on a monitor far more accurately than the human eye can. You should follow the instructions that come with the device and the accompanying software.
LCD monitors should have a brightness level of 100 to 120 luminance. Out of the box, all monitors run at a higher (some much higher), level than this. This is a standard setting when profiling the monitor, rather than a QBY one. Also it is important to set the gamma to 2.2 irrespective of monitor type.
At the end of calibrating the monitor, there will be an opportunity to compare the previous to the current profile. If the change is large, re-do it to ensure everything is correct. Also keep it current. Do so every two to four weeks.