Pronounce the S like the S in snake when it occurs between vowels. For example, "eso" is pronounced "esso" not "ezo." Pronounce the X as "ks" between vowels. For example, "examen" is pronounced "eksamen" not "ekzamen."
Pronounce B and V the same way when they occur in the same context. For example, "beto" and "veto" are both pronounced like the B in bottle. Pronounce the B or V by quickly and firmly closing your lips when they comes after M, N, ' or a pause.
Pronounce the B or V without ever fully closing your lips when the B or V occurs after any other letter than M, N, '. Your lips should come close to touching to form the B sound, producing a light friction. So "bebo" is pronounced with two different Bs: the first B involves a full closure of the lips and the second requires that the lips never close fully.
Pronounce the D like the D in "day," except that the tongue should come closer to the upper front teeth, when it occurs after M, N, ', L or a pause. Pronounce the D like the TH in "though" after all other letters. Therefore, in "el dedo," use two different D pronunciations. Something like, "el dethough."