As great as it is to Daven for others its even greater if the one in need Davens him/herself. See Rashi in Vayeira perek 21 passuk 17.
The main thing is for any Tefillah to be answered it has to be sincere and heartfelt and with tears. A Tefillah with tears is worth many many tefillos without tears. If you can’t cry to Hashem you haven’t even begun Davening.