The Mosque is so big that it can't be fully explored without a tour guide. On Saturdays, Tuesdays, Wednesdays, and Thursdays, tours start at 11:00 in the morning. On Fridays, tours start at 5:00 in the afternoon.
Also, ensure you always have your sunglasses because the temperature there can get pretty high. Choose a tour that starts early in the morning or late in the afternoon to have a humble time exploring the Mosque. During the tour, you will also have the chance to look around the Grand Mosque and learn more about it. You can also;
Worship: If you're a religious person, you're welcome to go to the Mosque when it's open for prayer.
Take in the beauty: The Grand Mosque is full of beautiful things to see, from the fancy chandeliers to the tall columns. During your trip, you should make it a point to look at every part of it and take a lot of pictures.
Stay until the end of the tour and watch the sunset: The best way to end the tour is to wait until it's over and then watch the sunset while sitting by the pool.
You should try to see the Grand Mosque both during the day and at night if you have the chance.