I remember making the time when LEGO used to put alternate models/ building ideas on the back of their boxes, and as a child it was one of my favourite aspects of the sets.
I cant provide you with instructions, but I will say that you should start with building the areas where the construction is shown relatively clearly in the image, for example, in this case the feet/ legs, arms, weapon and shield. The hips dont look too difficult as do the 'wings' on the back, you can see at least some of the parts needed to build these as well as the cockpit (and as its sloping, you'll need some form of hinge). You'll slowly start building up (sorry for the pun) a pile of bricks required for the build from the parts that make up the set. Youll have to 'fill in the gaps' using only the pieces that remain in the pile.
In some ares you'll have to be creative as the range of bricks are pretty limited, espeacially as this is a relatively small set.
So, good luck and hope that helps and sorry if this sounds obvious!