Unfortunately you do not write what kind of compunds from plant extracts you want to separate by using TLC. You also do not write about the type of stationary phase (polar/nonpolar) you intend to apply. You may read an excellent book written by a famous specialist where you can find the necessary information also about solvent selection and method development (and applications including plant extracts:-)
I recommend for you "Instrumental TLC", author: Colin F. Poole, Elsevier, 2015.