Sales 
No, seriously, it’s the sales periods that amount for most of the revenue of many publishers. Provided that you can get the asset into one of the sales. This means having a decent revenue in the 3-6 months prior and not frequently changing prices and such. I think the publisher guidelines have some details.
Then also 80% of the assets on the store are underpriced. Look for competing assets and by all means do not underprice them. Instead if you feel your asset is better than theirs, price it higher. Making a tool or template asset that doesn’t have a normal asking price of $50 or more is pretty much pointless (art, audio, etc assets are a little different). Most revenue is made by assets priced between $50 to $150, or even more.
50% off during the initial two weeks. Nothing else works better to get you in the “New and Hot” categories.
In the long run: frequent updates. If you let the asset just sit there and don’t invest in light of few sales, the sales will never ever pick up. Customers read assets with no updates as “dead in the water, stay away”.
Anything you can manage. I don’t think there’s a silver bullet. Make announcement wherever Unity assets are announced but be careful of the rules ie Reddit has a special place for Asset promos, they will delete your posts if you advertise in the regular Unity channels.
This is the key question!
Most assets advertise themselves as “easy, fast, saves money, adjective, adjective, superlative, detailed feature list”. This is guaranteed to underwoo potential customers.
First, ask yourself: why are you making this asset? What need does it satisfy, what pain does it alleviate if any? If you’re making a tool you got to answer this with utmost conviction. If you can make a trailer video showcasing the benefits of the tool, even better! Example keywords that most Unity devs would understand out of the box: prefab painter, hot reload, serialize anything, streaming worlds.
Grab them emotionally! Sometimes all it takes is ask a question most would answer in a certain way. Like:
“Are you tired of waiting for domain reload?” … instant interest!
Show, don’t tell!
A prefab painter that drops things on the terrain and it instantly looks good in a 5s video snippet is a sure seller. If you just write “place prefabs with ease, saves time” nobody cares.
A good practice to writing your asset description is to remove any and all adjectives and see what’s left. A good exercise is to pick some popular and some unknown assets and copy their descriptions, then remove the adjectives and other “fluff” words that sound good but don’t actually add anything meaningful.
Pretty sure the popular ones are still clear and convincing sentences without all the adjective fluff like faster, cheaper, powerful, innovative, and so forth. The bad description will end up reading like “This … tool … loads scenes and … workflow.” oh yeah, if that’s all, the marketing stint ain’t working! 
More tips and cautions mostly:
If you’re making yet-another-xyz good luck, nobody needs yet another of the same thing especially when there’s an already hot-selling #1 or even #2 and #3 assets you compete with. Don’t even try, pivot to something unique in that case! 
Avoid the overcrowded assets, like character controllers or “(insert game genre here) engine”. There are a few leftovers that are untackled but those you need to really dig deep whether they stand any chance of getting bought due to lack of developer interest / extreme specialization.
If you’re in some other category, like art, audio, etc … good luck. These categories are extremely challenging to get noticed so unless you truly provide AAA quality with all nooks and crannies AND uniqueness, you may not even get many views let alone sales. The problem with art, audio, and such is that there’s just too many publishers already doing that rather well and them usually being located in low wage countries, they dictate minimum wage prices upon everyone else. Plus you can get all of these non-Unity specific assets from other sites like CGTrader and a gazillion others, and quite often for very, very cheap.
Research your competitors. All too often development on an asset moves along only to find out as you publish that you’re not even half-way there in terms of features and presentation that a $25 asset already covers. This will be a hard sell.
Research your target audience. What do they want? Say, you’re making an online multiplayer game template that’s a 2d tile based retro game. Can you guess what’s wrong with that? I’d say those retro game devs ain’t looking for networking since the retro games themselves were rarely networked to begin with.
Don’t go overboard trying to support old Unity versions. I cannot stress this enough. Between Unity 6, 2022.3 and the only recently out of support 2021.3 these account for pretty much all of anyone’s sales. Nobody who is still using 2020, 2019, 2018, 2017, even Unity 5 is still buying assets specifically because it supports those really old versions. It’s just not a thing. In fact, it can be beneficial to support even the latest 6.1 beta and 6.2 alpha features if you have a good use case for it. Even going for Unity 6+ exclusively is a sound idea if your asset greatly benefits from a specific new feature.
You may want to quickly publish something cheap or free, just so you get to understand the review process and its duration, as well as being able to request and gain access to the closed publishers-only forum because there’s a TON more info in there. Like what the Unity version distribution currently is, and what customer preferences are in terms of genre and render pipelines.