I originally used Paint tool SAI but now I have a Mac I don't think I can get it because it isn't compatible? So for one of my artworks I had to use Photoshop. What I did to get my smoothish lines was I used the brush tool and used pressure sensitivity. It took a while to get the hang of but as long as you have got a decent brush selected then all should be good. I used a round-edged brush and then went to the Brush settings, went to the Shape Dynamics section, changed the control preset to Pressure sensitive and changed the minimum diameter to 0. You just need to be mindful of the pressure you are putting down on the tablet because if you change it suddenly, the line will not be smooth enough, but that depends on the sensitivity of the tablet. If there are any brushes that have certain textures you need theres an extensive amount of them on deviant art, some of them you have to give credit when you do art with it and some you can use freely, just make sure you check before you use it to know what the creator asks. :)