Most important for the success of your work is keeping to the gauge given in the instructions. Before starting knit a piece about 15cm wide and 8-10cm high in the pattern given for that model. Pull this piece lightly and with the edges straight, pin and cover with damp cloth, let dry. Compare the result with the gauge given in the instruction. Should there be a difference then use either thicker or thinner needles, in order to acquire the same gauge as given in the instructions.