i would say to definitely do a sketch beforehand very lightly, if you don’t it would be extremely hard to erase it and draw your finished product. i would also say build up on your shades don’t try and put them all at once gradually add more and more and make sure to blend areas necessary
Don't expect too much, go for your own style, erasers will be very handy, plan what the art is going to look like before you start it, experiment with texture and blending, keep practising.
