How do I draw a dot and cross diagram to show covalent bonds?

Start by identifying the atoms that are going to be bonded to each other, for example, two hydrogen atoms, and then work out how many electrons are in the outer shell of those atoms. Hydrogen only has one electron, so its outer shell has one electron. Electrons from different atoms want to pair up to make a bond, so each hydrogen will 'lend' an electron to the other, so between them they have two electrons, which is used to form the bond. This can be drawn as two overlapping circles, each with a H (for hydrogen) in the centre, and in the overlapping section, one dot, to represent the electron from one atom; and one cross, to represent the electron from the other.