Colour scheming can be a daunting exercise at the best of times but there are a few things you can do to achieve the desired result.
Take time to collect ample colour cards to select the initial colour scheme.
Invest in a tester pot or two when you have narrowed down your choices. This will allow you to stand back and take in the colour in relation to its surroundings. Light (or lack of it) can make a significant difference to shade.
Talk to the counter staff who are there to assist you with choices of paint finish and to give independent advice in relation to brand & cost