Basic Dot Diagram Rules

1.   Add Valence electrons
2.  Draw a skeleton structure (Usually put the least electronegative element in the center.)
3.  Subtract two electrons for each bond
4.  Distribute remaining electrons
Too many electrons?---put extra around the center atom

Too few electrons? -- put in multiple bonds


Other things to consider
Check formal charge -- Formal charge on each atom should be as low as possible. Formal charge sum on compounds should equal 0. Formal charge sum on ions should equal the charge on the ion.

(Valence electrons - 1/2 of shared electrons - all of unshared)  adjust skeleton if necessary to minimize formal charge----remember---no expansion of second series valence shells

Determine electron geometry  (count electron pairs (domains)  around center atom.

Remember, a multiple bond counts as one pair here)

Determine molecular geometry by considering shared and unshared pairs (total electron domains)

Remember --- a multiple bond counts as one pair here.
Determine hybridization by counting pairs---remember pi bonds eliminate the availability of a p orbital.

Find bond types by using electronegativity difference.

Determine molecular polarity by considering bond types and molecular geometry.  If centers of positive and negative charge are in different places, then the molecule is polar. (or if the sum of the charge vectors is not zero the molecule is polar).
Also relevant-- in oxy-acids, H's usually come off of O's.