Don't store any electronics in your shed as it will get quite cold over winter and warm in the summer which could lead to problems with the wiring. Don't store any damp/wet items in there as this will contribute to condensation and/or the growth of mould - bacteria thrive in conditions where there is a lot of moisture. Finally, don't store any super expensive items in there, as sheds are characteristically less safe than a house or a brick building, security-wise.