Personal preferences regarding R palettes in combination with ggplot2

Required Packages

Or just get paletteer, which is a fantastic package that collects most color palettes in R

Preferred palettes

ggsci

Futurama
NEJM
JAMA
UChicago

wesanderson

Darjeeling1
FantasticFox1
Zissou1

RColorBrewer

Dark2
Set1
Paired

virdis

virdis
inerno

Useful functions

scale_color_gradient(), scale_fill_gradient() for sequential gradients between two colors
scale_color_gradient2(), scale_fill_gradient2() for diverging gradients
scale_color_gradientn(), scale_fill_gradientn() for gradient between n colors
scale_fill_grey(), scale_colour_grey() are always a classic
scale_color_viridis() and scale_fill_viridis() for virdis color scales
scale_colour_brewer and scale_fill_brewer for brewer scales
colorRampPalette() can be utilized to produce a larger number of colors than those available in a palette

which subsequently can be fed to scale_color_manual() or scale_fill_manual()

e.g. scale_color_manual(values = colorRampPalette(RColorBrewer::brewer.pal(8, "Dark2"))(16))

Useful pages

Color-blind friendly palettes

colorblind_pal(), scale_colour_colorblind(), scale_color_colorblind(), scale_fill_colorblind functions from ggthemes package
Use display.brewer.all(colorblindFriendly = TRUE) to see the colorblind-friendly palettes of RColorBrewer
Both virdis and ggsci have colorblind-friendly options.

For more details check these pages