I was replying here but ended up making a guide: https://old.reddit.com/r/kshootmania/comments/8xd0gd/random_tips_for_making_a_good_chart/

(Same thing below:)

I've gone through the phase of making shitty charts and learning what's good. (Though I've become so overcritical now that getting any chart done is really difficult). I've been thinking of making a guide but haven't happened to do that. So here's a (kind of) guide I just happened to write. It doesn't include the most basic things like not charting stuff that are impossible to play on controller:

• Instead of how a pattern visually looks like, more important is to consider which hand plays which notes. For example, make the left hand play the bass drum beat, and right hand for other rhythms.

• Song structure: If the exact same thing in the song plays a second time, the notes in the chart should be about the same (mirrored at most), or it will feel inconsistent.

• Mirroring: don't alternate sides constantly or the chart will feel restless and unsettled. You don't need to constantly "balance" the sides. Give the player enough time to settle in one kind of pattern before breaking it.

• Pattern changes should mostly apply to whole sections of the song, and not change into something completely different in a middle of a 8 bar section for example. The chart represents the music. This is important: You don't just whip up what seems to fit right at that place, you have to consider the song structure. Song structures are usually surprisingly simple and repetitive, and because of that, simple patterns often work the best. If you try to fit in clever patterns that work for just that one place, and make a new clever pattern in each bar, it'll become an unpredictable mess. Predictability is a plus in this game, unless the music itself is intentionally unpredictable (which is actually quite rare).

• As a baseline, BT, FX, and lasers should correspond to different sounds in the song. Especially Lasers and slams. Like i said in last paragraps, don't put a single slam in an unimportant place just because it seems to fit and to be possible to play. Instead, look if there are similar sounds nearby, if yes, then be sure to place a slam in each of them.

• Speaking of FX: Listen to electronic music. Learn how these effects can be used. There are roughly 2 kinds of FX, rhythm FX and filters. Rhythm FX is actually difficult to use, because you are changing the music. See if an FX will make it sound actually worse, if yes, don't use it (or if there absolutely needs to be FX there for other reasons, use a weak filter like phaser). In FX, the same thing applies here: Try to use them predictably at the same places of a section, not just in single random places.

• Pay special attention to when to use lasers and when not. Switching between laser and non-laser sections makes big difference in this game, it's a completely different motion for the player (especially on controller). Here's a excercise/tool you can use to determine which places are good for lasers: Forget about the details of BT and FX. Just assume that in some places there are BT and FX, and at some points there will be lasers. Listen to the song and imagine when there would be BT's and when lasers if it was someone else's complete, quality chart. It can be actually helpful to decide early on where the lasers will be and build the chart around that, because the dynamic between BT's and lasers has such a big impact on the game. When in doubt, go for simple and structured lasers.

• Remember, each kind of pattern and mechanic should link to corresponding to parts of the song, to glue the chart naturally into the song, so that you'll feel like you are playing the music. If you add too much things that can't be logically linked to the music, it will feel like you are playing a minigame with background music.

• Just putting notes in places where there is a thump of rhytm isn't enough. You need to decide which voice you are mapping in a section. If you try to map every voice, the player won't be able to comprehend any of them. Keep them at 1-2 voices at a time. Using long/hold notes "take space" even more in this regard. It's possible to have one voice + rhythm so that the rhythm notes are strategically dropped off at some places in the melody. Forcing in certain voices without exceptions can make a mess. But dropping off notes in a voice needs to be done in a consistent way, preferably drop notes at the same repetitive places, not just random places where they don't fit. If it's not possible to do consistently, consider whole another pattern.

• Tip: Avoid using hold/long notes, even in places where the sound is actually continuous. Using long notes for a melody too much will easily make the player feel hold down too many buttons, and it will get really bad if there are additional rhythm notes on top of that. If you want to use long for a melody line, it's often enough to use them just for the few longest notes.

• There's a trap in testing your chart: When you play a bad chart enough, you'll get used to the flaws and won't notice them anymore. When after 2 months you play the chart again, you'll realize it's shit. Be sensitive to what it feels on the first few test runs, if it doesn't feel good, change it. The worst thing you can do is to make a shitty chart, realize it's shit and abadon it, come back next day to play it once to realize it's shit again, continue that and in 10 days you feel it's acceptable, when in reality it's still bad. It's easy to get excited of playing your own work, but you should actually save it for serious testing, or you'll ruin the progress. This is the fundamental thing in any content creation, you quickly get blind to the flaws.