Cut down on the amount you brush/comb your hair. Although brushing can be nice to keep your hair from matting up, it can also be harmful due to it breaking off hair.
Also, Stay away from chemicals (Bleaching,Dying,Relaxers,Perms, Etc.)
And Definitely Stay away from Heat tools (Straightening, Curling Iron/Wand, Blow Dryer)
Don't put your hair in ponytails and buns or tight cornrows (scalp braids) too often, as it can cause unneeded pressure on your hair.
If you want to go the 'extra mile' Invest in a good protein treatment (Ion Reconstruction works well and is available at Sally's Beauty Supply if you're in the states) although it will not make your hair soft, it will give it more elasticity, and strength. The olive oil is good, But try also investing in Moroccan oil and Argon oil, mix them together with the olive oil and heat it till it is as warm as you can handle, lather it in your hair, and let it sit for 1 hour while wrapped in foil. This will trap the heat in your hair and get deep into your hair shaft and cuticle and make your hair nice shiny and mend split ends.
As far as shampoo and conditioner go, it doesn't really make a difference to me, although i do prefer "Mane n' Tail" Brand Shampoo and conditioner.
Hope i could help!