Note: The skill level that each of these tips are directed to vary from anywhere between beginner-expert. In hindsight I should've kept it to one skill bracket, but it's too late to change it now LOL.
1) Dropping Vision
In order to use Brushmaker effectively, it's important to understand how bushes work. When a champion uses a targeted attack or ability while in a bush, they will reveal a 450 unit radius around them for 4.5 seconds. This also includes the area behind the bush that may have otherwise been blocked off. Additionally, minions' attacks will reveal a roughly 150 unit radius around them for 2 seconds.
There are a few implications to this mechanic. The first is that you should avoid needlessly attacking while inside your bushes, especially if you're against opponent(s) with targeted spells that require vision to cast. If you're experienced on ranged supports, you're likely familiar with the pattern of stepping out of the bush, attacking, and then slipping out of vision. This not only makes you difficult to attack, but also drops aggro from the minions wave. Getting into the habit of constantly dropping vision as lane Ivern is very important.
The second thing we can understand from bush revealing is that you don't want either teams' minions inside your bushes. Since both teams' minions will reveal the bush, making sure that you place your bushes away from the minion wave is important. There are a few cases you'll run into where placing your bushes on top of the minion wave are good (such as when you're the mid laner and you don't have enough information to lean to one side), but only do so after you understand the risks.
The final thing to take away from this is that when you attack from a bush, it won't reveal the whole bush. This doesn't have many practical uses, but it's nice to know for when you create longer bushes. You can attack from one end and retreat to the other to drop vision.
2) Free Bush Charge
Due to some weird programming quirk, Ivern's W will actually charge even if you haven't put a point into it. This is normal for abilities with charges that don't start with full stock (such as Jhin or Caitlyn traps), but Brushmaker gets 3/3 charges right when you level it.
This means that if you put a point into W before 1:15, your first bush will not consume a charge since it's using a hidden 4th charge that was prepared while the ability wasn't levelled. In matchups where you know you're starting W, make sure to level the ability early to claim your extra bush. This mechanic was definitely not intentional, but it's a free bush so I'm not complaining.
3) Bush Attack Timing
On the topic of weird programming quirks, Ivern's bush autos also have some really strange behavior. Contrary to what you might believe, Ivern doesn't actually shoot empowered autos from having the bush buff. Instead, the buff will empower the hit on impact. This may not seem significant, but there's a few reasons why it's important.
In lane, understanding this interaction extends the amount of time you're able to stay outside of your bush. Instead of your maximum number of autos being 3 before having to refresh the buff, you can get 1 last attack in right before you re-enter the bush. Having slightly more varied movement helps a lot in dodge-heavy matchups like Syndra or Ziggs.
This interaction is also why you're able to bush yourself and auto attack immediately after before the bush has finished spawning.
Note: I'm pretty sure this weird behavior is an unintentional artifact left from when Ivern got changed to a permanently ranged champion in patch 9.20.
4) Summoning Daisy
One of the major strengths of lane Ivern (especially top/bot since the lanes are longer) is his ability to unexpectedly run you down with Daisy. This is not only due to having a lot of CC, but also because of Daisy's movement speed buff upon being spawned. In order to catch your opponent off guard more often, get into the habit of hiding Daisy's spawn. There's 2 ways to do this:
The first is to stand on one corner of your bushes, and then summon Daisy towards the other. The positioning can be kinda tricky, but if you do it right Daisy will be completely hidden and ready to catch your lane opponent off guard.
The second method is to stand behind your bush and summon Daisy into it. Summoning her this way is a lot faster and doesn't require any precise positioning, but you'll have to make sure they don't have vision of you or they'll hear the sfx/voiceline of Ivern's R cast.
5) Short Trades and Bush Disengage
For my last tip on this list, I'm gonna mention something a little more advanced. Up until recently, my engage combo as Ivern would consist of landing Q, putting a shield on myself, dashing in, and casting W on my destination during the dash
(Q₁ → E → Q₂ → Wᵗᵃʳᵍᵉᵗ → Auto)
The problem with this is that if you're going for a shorter trade, you lose control of your bush as you disengage. This limits your ability to auto attack and kite back since your opponent is now hidden inside your bush. I've recently been using a modified version of this combo for shorter trades where you bush in the middle of your dash path, pull yourself through it, and then kite back in:
(Q₁ → Wᵖᵃᵗʰ → E → Q₂ → Auto)
This makes it so that instead of making it harder for you to disengage smoothly, the bush position makes it easier. Despite it's strengths, it's still only useful for shorter trades since you're forced to retreat back if you want to keep your empowered autos.
This is a very useful combo to know and it helps a lot against champions who want to trade back onto you with autos or targeted abilities such as Gangplank or Teemo.
Anyways, thanks for reading as always! I haven't been posting as much recently, but I plan to get that frequency up to around once or twice a week. Only time will tell if I can actually pull that schedule off (I'm kinda lazy when it comes to these things).
I've also finally added a comment section to these posts, so if you have any questions or requests for future articles I'd be happy to answer them!