To get enough rocks, in practice mode(which can be found in the multi-player option at the main menu; you should have tech level to 7), send a Trike to look around. Also, look for the amount of Spice nearby. If you have a sufficient amount of Spice and Rock, find a place for your MCV. If you do not, press ESC, select "Abort Mission", and reset the campaign. Repeat this process until you are used to your environment. Do not look for another place without resetting the mission, as it wastes time and your enemy or enemies can find you and launch an assault.