Intent to return to home couuntry could be shown by strong family ties, property, bank accounts in home country, job offers in home country, invitation to interview by companies in home country, detailed explanantion of how your education will benefit you and/or your home country, etc.
For COS to F1, the INS would either approve or deny. This is unlike COS to H1 filed by an employer, where the INS could approve the H1 petition, but not the COS, and so you could be asked to go out of the US, get an H1 stamp, and then re-enter. In this case you get an approval notice without an I-94 at the bottom. For COS to F1, this is not the case as the I-539 application is yours, and not any employers. Its either approval or denial.