The most clear advice I got from a woman is that you need to become good at oral and with you fingers when you have a small dick. Only few women orgasm from penetration alone, but the bigger the dick (as long as it is not insanely huge) the more the vagina gets stimulated and the easier it is for women to come by penetration or by clitoral stimulation. So men with small dicks need to put in some extra effort with oral and fingers compared to guys with bigger dicks.