This section includes a few useful bullet points to keep in mind when writing your own missions;

• Using the original mission code
  The best way to learn mission code is through the original. If there's something you see in the original that you don't know how to do, then have a look for it in the mission code. The best way to do this is to remember a briefing message around the code you want to look at. Then open up the FXT file, find the relevant peice of code, then do a search for that number.
  
  
• Set the player line to a memerable one
  It's a good idea to set the PLAYER line to having a memerable line number. You will have to refer to it quite a lot during the mission code (such as setting a peds enemy), so with a memerable line number you won't have to keep checking back. Something like 666 you won't forget.
  
  
• Working out survive lengths
  You'll be using SURVIVE's loads in your missions. Remember, there are 25 survive 'ticks' in a second - so ten seconds would be a SURVIVE of 250. Also remember that for kill frenzy times on a POWERUP, you need to add 100 to this number.
  
  
• Creating kick ass insane stunt bonuses
  Everyone loves insane stunt bonuses, so it's worth the effort to create a few. The trick behind doing them is the downwards slope 'feature' in the GTA mission engine - if a vehicle falls and lands on a slope (in either direction) then the damage is set to 50. This way, you can create a huge jump and get the player to land safely by setting up a small slope as a landing pad!
  
  
• Set out your mission code correctly
  It's important to number your code in the best way. Renumbering your code is a horrible thing to do - take my word for it. Leave gaps of 5 or 10 inbetween each line. Set each mission to a group of 1000 lines, both in the mission declarations and the code (so mission 5 will have lines 5000-5999 in the declarations and mission code, for example). Set a section for your kill frenzies, insane stunt bonuses and respawning powerups (such as 20000-25000, 25000-30000 and 30000 onwards).
  
  
• Make a powerups and triggers procedure
  You need to turn on all your powerups and disable most of your triggers right at the start of the mission. The best way to do this is launch a KICKSTART straight after the STARTUP line, say to line 35000. Here you can list all your DISABLE's and POWERUP_ON's. set 35999 to a do NONOWT to stop the code.
  
  
• Ensure all your files are easily excessible
  When writing missions you need a lot open - the map file, the MTD.doc, the mission.ini, the english.fxt etc... it's a good idea to setup a quick way to launch them all. I setup a program group in the start menu with links to the game and app the files that I use. You may also find it useful to use a mod-launcher to make it easy to test different mods.
  
  
• Keep your mission positions close
  When writing a mission, it's a good idea to keep all the points close together. For example, if the player has to go to a phone, pick up a car and take it to a garage, put all the points in the same road or area. That way you can quickly test each section. Once you're sure everything works perfectly, space everything out and test the difficultly of the level.
  
  
• Try and be diverse
  My one main criticism with the original is that the game became extremely similar - get a car, kill that guy, pick up so-and-so, go to the garage etc. Once I got the Vice City I wasn't interested in the missions. If you're setting out making a mod, try and be original with your storylines and settings to make things more interesting. Mods like Spacestation GTA and Snowball City are good examples of this.