The trigger mechanism is very simple, the bar(25) is pushed rearward by trigger movement, the tab on top slides over the striker block safety(8), overcomes the striker spring(6) tension as it brings it to full cock position, aided by the trigger spring(34). This is the takeup stage, a light, but long pull, when the tab on the back of the trigger bar reaches the angled face of the connector(23) it is pushed down, and the tab that is in contact with the bottom of the striker(4) slides off, allowing the striker to fall. The pistol fires, the slide moves rearward and a channel in the slide that the tab on top of the connector(23) rides is has a bump that pushes it over, allows the trigger bar to slip past, rise up, and catch the striker as the slide comes back into battery with a fresh round. At ths point the trigger bar is next to the connector, not in front of it as it would be in order to engage the ramp and fire again, so the trigger has to come forward a short distance, the connector snaps back behind the trigger bar, and you can fire again with the short reset, making followup shots fast. To render the pistol "safe", you siply release the trigger, the striker lowers to 1/2 cock, the pin safety blocks the striker, and the trigger paddle locks the trigger.
You can modify the trigger, or more accurately different parts of the cycle. You can easily reduce overtravel and shorten the reset with a trigger stop, leaving all else unaffected. You can reduce the first stage takeup weight with a heavier trigger spring to assist pulling aggainst the striker, you can also lower the weight of both stages with a lighter striker spring, with a potential loss of reliability. The connectors are one of the easier, and more popular options for changing the second stage weight, and length. The angle of the ramp affects this, like pulling a sled up a hill, the shallower the angle, the lighter the pull, but the more creep and longer second stage pull needed, a steep angle increases the weight, but makes the pull shorter and crisper. You also have to overcome the striker safety button, it comes rough and steep, but can be rounded and polished with no affect on reliability, and alone makes the trigger lighter and smoother, the spring in it can also be lightened with a potentially dangerous loss of theis safety function as a result. There are contact areas on the bar and striker where metal moves aggainst metal, polishing these areas reduces friction loss, keeps dirt from sticking, and both smooths and lightens the trigger with an actual increase in reliability. The more extreme modifications involve changing angles, or materials, some nodules even have adjustments, they can give a great trigger, but can have problems with reliability or safety if not set properly. In many cases you have the option of modifying existing parts, installing factory options, or using aftermarket parts, all need to be competently worked, and tested thoroughly for safety and function.
You must also keep in mind what your purpouse is with the pistol. If you are skilled, and using it for competition with one brand/model of ammo, radiused and lighter safety button, aftermarket or reworked factory trigger, heavier connector, heavier trigger spring, lighter striker spring, overtravel stop, this will give an extremely light takeup, short crisp break around 5#, and short positive reset. If you are going to use it for defense, then some polishing, perhaps a radiused safety button, maybe a heavier trigger spring or trigger stop, perhaps a couple tweaks and improvements with extractor angle and ramp finish to improve reliability and nothing more unless you are confident in the reliability of the mods, this gives a little lighter takeup, more abrupt second stage, shorter reset, and smoother pull. For a range pistol that won't be used for defense, but will see a variety of ammo, then you can go pretty much the same direction as the competition trigger, but without a lighter striker spring, or lighter safety button spring, these mods just aren't worth the trouble outside of a few circumstances, and even then they must be carefully tuned and checked to make sure they are safe and function well.
There is a host of options for GLOCK triggers, and in many cases it comes down to personal prefference, some aftermarket options change it to a short "single action" feel, that some like, the NY1 and 3.5# connector gives a nice light "DA revolver" feel, long smooth pull with a barely noticeable break stage. I personally like the 2 stage feel the pistol was designed around, although I do like it to be a bit more pronounced with a lighter takeup. This helps keep your finger on the trigger with some weight to pre-stage your finger, and the short positive reset makes it a fast shooter.
