1) If one wants to fix a certain amount of learning, or to fulfil a certain commandment, and he is worried that after a certain period of time his resolve to do that thing will weaken, or if he is worried that he will commit a certain sin, he may encourage himself by making a vow or an oath. (Kitzur Shulchan Aruch 67).
2) Even if one did not use the expressions which signify a vow, and one said just that one will learn a certain study, or perform a certain commandment, it is considered to be a vow, and one must fulfil it. Therefore, a person should accustom himself to say clearly that any positive act that he says he will do will be done without an oath. Even when discussing doing mundane matters, which are not commandments, one should accustom oneself to specify that it is all without a vow, so that he will not end up blundering into the sin of making vows.