1. Select any ship (maybe third one is the best for this since it is fastest)
2. Get a power-up that you find the best for fast clear (one of the weapon power-up's ofc; personally i have chosen fast autofire one, 3-shot is kinda slow, or maybe bouncing one is not bad but it doesn't drop frequently)
3. Before the power-up expires, press ESC and choose select ship (at this point i suggest ship no.2 but you can take first or last one as well)
4. Now your game will start with the previously chosen infinite power-up!

1. After you started new game with the infinite power-up, the key is to get combo that multiplies your score (x10, x50, x100 and more) as fast as you can, and you get it by taking down enemy ships. I say as fast as possible because enemy ships become diversed and harder with time. Keep in mind that after several seconds without taking down an enemy ship you lose combo multiplier, and that will slow you down. Along with new types of enemy ships that start to appear, your chance to get score of 100.000 will be lower.
2. General advice is to be as precise as possible, also don't forget to use right click (power shot) frequently. Also, use space when necessary to run away, it saved me many times. If there is too many ships around you, try to make circles around and take them down with right click.
3. If you don't lose combo and take down enemy ships fast and accurate enough from the beginning with your infinite power up, getting score of 100.000 shouldn't be a problem.

I hope this guide will help you make easy 100% achievements in this game, and avoid your rage (happened to me, that is why i examined this game deeper and wrote this guide for you). If you have any questions, suggestions, feel free to leave a comment or just add me and ask whatever you need.

Cheers!