This page of the Grand Theft Auto V guide provides general information about the mission types available in the game. You will learn about the objectives of each task and whether they are required to complete the main plot of GTA 5.
The walkthrough descriptions of the main missions have been published in the s guide, more or less in the order that they are unlocked by the game. Still, it is worth knowing that you do not necessarily need to complete them in that same order. What is even more, the missions connected with assassinations, which you are tasked with by Lester, (23: Hotel Assassination, 24: The Multi Target Assassination, 44: The Vice Assassination, 45: The Bus Assassination, 50: The Construction Assassination) can be left for later. Personally, I recommend that you take to them after you have completed the last big heist (The Big Score) because, with several/tens of millions of dollars on your pocketbook, you will be easily able to multiply your assets and, as a result, buy all of the available estates.
At the same time, it is worth noting that it is impossible to complete all of the missions contained in this guide at one sitting, because many of them are bound with specific heist variants. Personally, I recommend that you save the game before you start your preparations for each one of the major heists, which will enable you to check out on all of the missions and, at the same time, select the heist variant that you consider more profitable.
Strangers and freaks
Successive missions from strangers and freaks are unlocked as you make progress in the game but, there is no one specific moment at which a given mission becomes available. That is why I recommend that you check out on the map frequently and make sure that the locations, in which the question marks are supposed to appear, are discovered early enough (fortunately, most side missions take place in Los Santos and Sandy shores).
Many of the stranger and freaks missions come interconnected, and it is usually the case that the next mission from a given person becomes available after the previous one is completed. Many times you will also need to wait for several hours, or days, until it is available.
By analogy to the main missions, most of the side missions can be repeated from the level of the pause menu. The exception to this rule are the missions which consist only of listening to the person in question (e.g. the initial meeting with Omega, Abigail or Nigel).
Random events become available at various stages of the game and they start appearing already in the initial hours of the game. Most of them start in specific locations but, not necessarily after you visit that location for the first time. If this was the case, you need to visit that place later in the game, in hope that the event reappears.
Unlike the main missions, or stranger and freaks missions, random events cannot be repeated from the level of the pause menu. It is worth knowing, however, that a given event does not repeat if you complete it properly. Several of the events (e.g. attacks on marijuana plantation, ATMs), follow a cyclical pattern, i.e. they repeat on a regular basis.
Property missions become available only after you purchase the appropriate estates. Most of the missions connected with estates are random in their character, i.e. you can practically at any moment in the game, receive a phone call, or a message with the information of the availability of a new mission. You, of course, need to be playing the correct protagonist for that to happen - while playing, e.g. as Michael, you will be receiving information from the managers of the estates that he bought, while Franklin's and Trevor's estates are inactive.