I had hit a plateau with fireworks, scoring between 210,000-220,000, when I decided that I had to change something I was doing.
First, I shut off any extra programs running on my computer that might slow it down a bit. I fiddled with the colors in my display setting and changed that from 32 to 16. If I have been on the internet for an extended period of time, I will often clear the cache before logging onto vmk. I guess what I'm saying is do anything you can to optimize the speed of your computer. I also changed out my mouse for a new one that we had on hand (same style, but maybe a little fresher). A wireless mouse may be "slower" than a wired mouse.
I thought maybe I had developed some habits/ways of clicking at the fireworks that were not very accurate. I don't try to position the cursor directly over the firework now--there is an area of effectiveness (perimeter) around the cursor that allows for the same score as if the cursor was directly over the firework when clicked. I can keep my cursor a little to the right of the firework so that I can see the actual timing of the star flash better. I also changed the amount of pressure I use on the mouse button when I click. I used to click quickly with a light touch. Now I use a more firm press of the mouse button. I think by doing this I gain the extra fraction of a second that makes the difference between awesome and flawless. I do click a lot lighter and quicker when there is a large volley of fireworks at the same time, like at the end of the game.
Then I realized that I had developed the habit of scrolling through the fireworks symbols from left to right, using the right arrow key. Actually, sometimes it is faster to get to the correct symbol by scrolling "backwards," using the left arrow key. I can now judge which arrow (right or left) to press so I get to the next symbol by the fastest route.
Also, be aware that there is a difference in how fast each of the colors of fireworks detonates. I have identified what I consider to be three different speeds. For example, the slowest fireworks to detonate are the pink, green and yellow. The fastest are the last two colors on the right, the teal and blue. The other colors are kind of average in speed. Other people may have different observations of course, but being aware of the detonation speed helped me a lot.
Try to get rid of any distractions that may be going on around you when you play fireworks. Lol, I have "kicked" my kids out of the room, turned down the tv, shut off the ceiling fan, etc.
Lastly, as the others have said, it just takes a lot of practice. I am no expert and don't get my name on the high scores list, but by making these changes to my method I have improved enough that I have quite a few fireworks magic pins.