There is nothing you need to do before getting married in the Philippines. Are you planning on bringing your future spouse to the U.S.? For immigration purposes, you will need to file for her to come to the US on an immigrant visa. Because you are only on a green card, it will take longer for a visa to become available. You should start with the filing of the I-130 petition and then when the visa becomes available, go for the immigrant visa with the U.S. Consulate in Manila.
You don't need to inform anyone before you get married. After you are married, you are eligible to apply for a green card for your spouse. The process will take some extra time, but the current wait for an I-130 to become current is about six months, the processing time takes about an additional year, but can vary greatly case to case. Your spouse will not be able to come to the US during this time, unless she has a different visa. The process when a person lives abroad can be a bit complicated, as it involves the Immigration Service, National Visa Center, and foreign Embassy or Consulate. You may want to consult an attorney for assistance. Congratulations and good luck!