After Hashem told Moshe and Aharon to go to Paroh and have him release Bnai Yisrael from Mitzrayim, the Posuk says that Moshe and Aharon did as Hashem had commanded them (שמות ז:ו'). Rabbi Yosef Karo, author of the Shulchan Aruch, notes that Moshe and Aharon in fact did not do as Hashem had commanded them just yet. It was not until later on that they actually went to Paroh to convince him to free Bnai Yisrael. They rather only accepted this commandment upon themselves at that time, but nevertheless the Torah (שם) states "כן עשו," "so they did," because this sincere acceptance on their part is considered as a fulfillment of the commandment. Since they said they would do it, it was as good as being done already.
Whenever one sincerely accepts and plans to do a good deed, one should already feel the joy of doing a Mitzvah although he hasn't yet done it. On the other hand, of course, planning alone without taking action will not amount to much. But when one does the Mitzvah, the joy of actually doing it will be even greater because of one's anticipation of performing it. This will also demonstrate one's appreciation for doing even more Mitzvos in the future.
A story is told of Rabbi Yeshaya Cheshin, a Rav who used to Daven in a certain Shul in Yerushalayim. One Simchas Torah, during the Hakafos, when all the singing and dancing was going on, he noticed that there were a few workers sitting on the side who did not participate in this joy. Rabbi Cheshin approached them with a pleasant and joyful face and invited them to join. The men answered by saying that those who study Torah have something to be joyous about, but they did not study Torah for a whole year, and therefore did not feel part of the joy.
Rabbi Cheshin then replied by explaining that on Simchas Torah, there are two Chassanim: the Chassan Torah and the Chassan Bereishis. The Chassan Torah represents those who have learned Torah the whole year and are happy about it. The Chassan Bereishis, on the other hand, represents those who have not studied during the previous year, but have accepted upon themselves to study during the upcoming new year. Those people too can be joyous because of what they plan to do. He therefore invited these workers to join them and experience the joy for the future. The workers felt very positive about this, and said that they were willing to accept this Torah study upon themselves, but needed someone to teach them. Rabbi Cheshin assured them that he would teach them on a regular basis, and they right away joined the singing and dancing. We see from this story that one can take pride in one's plans and can be inspired by this to accomplish great things.