composing
This text assumes that you are a non-asalato player looking to write for the asalato, and that you have some familiarity with composing for concert halls/settings.
writing for percussionists playing the asalato
do not make random percussionists play an air-turn
The most that an untrained concert percussionist could do are the techniques listed as easy on the technique index. The vast majority of percussionists cannot play the asalato proficiently. Do not write medium difficulty asalato parts (such as any rhythm that uses an air-turn) and give them to a concert percussionist assuming that they could play any percussion instrument.
do make random percussionists play the asalato
You can make percussionists play the asalato, because generic shaker technique (such as egg shaker technique) is transferable to asalato. There are also quite a few techniques on the technique index that are listed as easy, and it's possible to experiment with musical ideas.
asalato is not a common instrument
Most percussionists will not own a pair of asalato or know where to get one. Be sure to either provide the asalato or provide resources to acquire asalato if you are making percussionists play asalato.
writing for asalato players
Above all else, if you are writing for the asalato, it is recommended that you already have a specific asalatist in mind who is ready and willing to play your music, and tailor your part to that player. This is because the experiences and skillsets of asalato players range wildly—something that is easy for one player may be very difficult for another.
This means sitting down with your asalato player and talking about what their preferences are in terms of notation and techniques used.
This doesn't have to be limiting. Maybe they say "anything is fine!"
However, here are some general ideas that may be useful.
orchestration
volume
The asalato is a fairly quiet instrument. It is quieter than most maracas and castanets. The shake sound projects slightly less than an egg shaker.
There are a few different types of asalato:
Gourd asalato are at a medium dynamic, but can be used when amplified. They have a warm timbre.
Plastic asalato are the loudest types of asalato, and have a very bright timbre.
Cork and cord asalato (and any other asalato considered "manner mode") are meant to be used for practice in spaces where it is not acceptable to make loud noises, such as in an apartment. They are unusable in ensemble settings unless amplified.
Wooden asalato are similar to gourd asalato, but are a bit louder and brighter, depending on the maker. However, they are somewhat uncommon.
No asalato currently on the market can project over instruments such as a trumpet or drum set.
Additionally, certain techniques have limits on how loud they can be played: namely all shake types and all variations of flop click, among others. The techniques listed as "low volume, low range, low ease" are usually only used in solo playing, when amplified, or when only playing with other asalato players.
technique order
Certain techniques cannot be chained together, as they start and end in different positions. For example, it is impossible to play a snap click right before a flop wrist click without any extra sound or time to move the gourds around, because the end position of snap click is flip position, while the start position of flop wrist click is flop position.
This makes it very hard to write for the asalato in an idiomatic way if you do not play the asalato. If you are careful with matching start and end positions, it can be possible.
tempo
Asalato is unique in that certain techniques are easier at certain tempi. It is very difficult for an asalato player to transition smoothly from slow to fast (or vice versa) with a complex comping pattern.
visual location
The visually interesting aspect of the asalato means that it can be important to think about where the asalato player will be placed in the ensemble, so that their playing is visible to the audience.
notation
if you are writing for an asalato player who cannot read Western staff notation
Create a document similar to a cheatsheet that a musician in a band might use, and include indicators on style, or markings such as "unison with marimba here". Work out names between you and the asalato player of specific grooves or styles that you would want to use.
Here's an example:
four on the floor groove for 16 bars
flip-flop delay + variations for 35 bars
solo fill for 1 bar
if you are writing for an asalato player who can read Western staff notation
Create a score similar to a drum set part that is mostly comping, and notate hits when needed.
if you are writing for a percussionist playing the asalato
Create a score that looks like it would be for a multiple percussion (multipercussion) solo. The examples on notation (aside from glyph notation) are useful here. However, none of those systems are used widely. If you make a notation system, it must include a key explaining what each notehead is.
other skillsets
The international asalato community has some overlap with the skill toy community as well as the concert percussion community. It may be interesting to see what other skills your asalatist has and could incorporate in a piece of music.