So a lot of people have been asking how exactly heists are performed, specifically with friends and crews. So here's the breakdown. For the sake of argument, lets go ahead and define what heists and robberies are. A "heist" is larger and planned mission to steal from a bank, jewelry store, etc. A heist will have multiple phases and will usually require multiple people to help out. A "robbery" is a small job, usually capable of being performed by one person, and involves a quick and unplanned attack on a smaller business, like a gas station or liquor store.
Heists are GTAO missions and robberies are performed in free roam at any given time.
Robberies are pretty straight forward, so we won't talk much about them. They involve running into a store and stealing from the clerk. Fleeca Bank locations are considered to be robberies (although do appear in missions) and do not require planning, although getting the money requires opening the vault inside the bank and therefore may take longer than a smash-and-grab job on a liquor store, so bring along some muscle to watch your back. Same thing goes for armored cars, they can be robbed any time in free roam but will also be the center of attention for some heists.
All about heists:
You can perform heists with your friends, crew and even NPC's. Since heists are actual GTAO missions and function very much like in story mode. Any player, whether in a crew or not, may perform a heist. If, by chance, none of your friends or crew members are available to help, you may choose NPC's known as "contacts" to help you with the job, however the contacts will not assist you with the prep and planning, so that's all on you.
Once you have chosen a heist, i.e. a bank job, you then get to pick who you want to help you. If you pick a fellow crew member or friend, they will receive an invite to join you and then they become a part of the planning phase.
As the leader, you get to assign roles and tasks to the people who help you. For example, if the heist requires the use of a helicopter then you can pick a crew member who already has a helicopter, then therefore it's their job to assist with the flying. Or, if no one has a helicopter, then you assign someone to go steal one. Similarly, you can assign people as getaway drivers if they have the better driving skill, muscle if they have the better shooting skill, and even snipers if you need them.
Once planning is done and all assets for the heist are acquired then it's time to take action. Since this is a mission and not a robbery in free roam, it can result in a failure, but fortunately can also be retried. The leader can assign a difficulty level to the job and how many lives are available. This difficulty has an effect on skill points, so the harder a job you perform then the more skill points you will earn.
Once a heist is done it's time for the getaway. Although there are ways to master heists and thus perform them without alerting police, most jobs will result in a chase, so make sure you hire a good driver and you have a getaway route planned in advance. The heist is over once you've successfully escaped the police and at that time the leader decides how to divvy up the money. Everyone can get an equal share, or may be paid based on their performance and how much work they put in, or the leader can betray everyone, kill you, and then take the money for himself. Obviously the latter of those options may have consequences later on.
If you hire NPC's to help you, they are always paid a cut depending on their skill level no matter what, just like in story mode. There are also measures in place to prevent abuse of the system. Specific details won't be shared, but players will not be able to redo the same missions over and over again to keep getting the same payout and skill points every time. Rockstar wants players to always experience something new in GTAO and things like "stat padding" have been thought of in advance and will not be tolerated.
Note: The ability to visually plan a heist like in story mode will depend on the type of property you own. If you're a low budget crook then don't expect too much in the ways of proper planning, but if you're a pro and can ball hard then the ability to strategically plan your caper is at your fingertips.