my first PS sketch

hi! guys,long time no see.finally i have started work in photoshop.this one is my first sketch in PS.please do tell me how it is.well i am getting problem in colouring this image.when i do colouring,there are patches of colours left and colour gradation(like colour do not mix with eachother e.gshades of skin colour do not mix with each other) is missing.there is no smootheness like xia sketches.please give me some tips how to start colouring.this sketch is inspired from carlos cabrera work.