Biotin and Zink will help extent the growth cycle of your hair (your hair naturally grows and then goes dormant for a while which isn't normally noticed as other hairs become active at that time but by extending the growth cycle you will have more hair growing at any one time making your hair seem thicker)...
Hot jojoba oil treatments are also supposed to help by keeping the pores in the scalp open and healthy as it is anti-bacterial and effects the body's natural sebum production by naturally clearing away chemical buildup and being absorbed by the hair and scalp making the hair softer and less likely to develop split ends.
Getting your hair cut/trimmed regularly will also help you grow longer hair which I know sounds like your working against it but really what your doing is preventing split ends which makes the hair weaker and far more likely to break (much higher up then you trimmed)
Washing your hair regularly is so important to your hair growth its not even funny and the real reason is that you are washing your scalp and removing dirt and contaminates that will lead to clogged pores and hair follicles (causing slow growth) I'm sure some one will swear not washing their hair helped them but likely that was because it helped keep their hair moisturized (preventing split ends/hair breakage) but that growth was likely much slower then it could have been if they washed their hair and followed the simple hair care steps I'm outlining here.
When your washing your hair use a colder setting in the shower as hot water will strip the hairs of its natural moistures and make it weaker and more likely to break (hair is naturally weak when its wet but even weaker when it hot and wet) when drying your hair treat it carefully as its at its weakest (get a High Performance Drying Towel such as the ones used in car detailing and just wrap your hair with it and let it absorb the moisture) then with your hair is mostly dry (usually in minutes) put it up or blow and style it.
These are just suggestions and can all be confirmed through simple searches on the internet... I hope they help you out