Create a ‘Long List’ of colours that complement items such as windows, furniture & curtains.
Narrow to a ‘Short List’ using this site to eliminate colours that don’t suit at a larger scale.
You can now move onto real paint samples.
Consider getting each colour in a lighter shade as well. When painted to a bigger scale colours can be more intense.
Don’t paint samples directly onto the wall, buy some Lining Paper.
Each sample should be a square of around 50cm on each side (the width of the lining paper).
A 100ml paint sample will do two coats on three 50cm square samples.
A 10m roll of lining paper is long enough for 3 sample squares for 6 colours.
Write the name of the colour on the back on the sample for easy reference.
Once dried, put the samples up with Blu Tack in different locations; by the window, in the darkest corner and by a key piece of furniture.
View the colours at different times of day as they will look different as the light changes, including at night under artificial light.
Write notes on the back of the lining paper with your views on the colour in that position / light condition. For example: "By window, early morning light, shade too dark and tone too green against curtains.”
This can help if your 'Short List' is quite long or if none of them hit the spot.
You should be ready to choose your ideal colour, or at least can continue to iterate this process until you do.