Three words - practise, practise, practise!
There are lots of books out there which will teach you basic drawing skills such as perspective and anatomy and such like.
Also look out for online tutorials on You Tube etc.
Most importantly, though, get yourself an A4 sketch pad and sit and sketch what is in front of you - a shoe, a vase of flowers, your mum watching tv, whatever. Or look out the window
and sketch what you see, with emphasis on "sketch" - don't worry about shading or colouring to start with, and keep them small. With figure drawing, start by doing a cartoon version
of someone running or whatever, then redo it by making it a bit more realistic each time. Try and do something every day, even while watching tv, for instance.