Go to lospec and have a look through the palettes. Notice how so many of the ones that are popular are very small, most palettes are around 16 colours.
Smaller palettes are great, they may be more restricted but this limitation makes it both easier to use and also more cohesive. Always cut redundant colours
My tip is to start small when building palettes. Choose a handful of hues you want in the palette (eg brown, blue, green) and build small ramps of colour for each one from dark to light. Try to reuse colours across different ramps where possible.
Important note:
You can think of colour as being made up of 3 components, hue, saturation and brightness. Focus on hue and brightness for now and try not to overthink saturation since that’s more difficult.
BRIGHTNESS
The overall trend of a ramp should be from dark to light, it’s brightness increasing (think of it as like black to white if it were in greyscale) This can change depending on how pastel or dark or contrasty you want the palette to be.
HUE
The hue of a colour is closely related to its position on the colour ramp. Darker colours tend to be cooler, tending towards dark blue on the hue slider
Brighter colours tend to be warmer, tending towards yellow
(this is because shadows are not in the warm light of the sun, this helps make these hue shifted palettes feel warm, vibrant and realistic, impressionist paintings are excellent examples of exaggerated hue shifting like this)
Examples:
warm blue is turquoise, cold blue is ultramarine blue
Purple → Red → Orange → Yellow is getting warmer.
Yellow → Green → Turquoise → Blue is getting colder
SATURATION
Saturation is an interesting one. I usually like to keep the saturation low up the ramp (where the brightness is high) and increase it down the ramp. (Mimics exposure from strong light) Saturation can be heavily changed through, red line palette has full sat high up in the ramp. Human skintones usually have the saturation peak in the middle of the ramp. So with saturation follow the general rule of get less saturated if it’s very bright but it’s quite a flexible one. This also goes with the other rules, there’s palettes with low brightness changes that are carried by big hue shifts and vice versa.