Keep in mind the Threats & Synergies section is based on each champ in their main role (or at least where I saw them the most) and is listed in order of Jungler > Mid > Support > Top > ADC then alphabetically

0. Start 99% of the games topside and path bot, the 1% are the very rare cases when the enemy bot comp is not gankable whatsoever
0.1. Always look to gank mid after clearing 3 camps of your jungle quadrant if : your midlaner is being pushed in and/or the enemy midlaner doesnt have an easy way to drop your frenzy and escape. If neither of these occur, dont bother and simply continue to full clear into looking for a bot gank
0.2. You're extremely good at soloing the objectives, make sure you have enough vision on the enemy jungle and laners to avoid getting ganked. You can also contest most junglers 1v1 on the objectives that they're soloing, given that they are not fed/outscaling you and/or you land your R on them. (For simplicity, you can contest all junglers that I put into Even or lower as threats. Exceptions for ones above Even that you can attempt situationally are: Elise, Lillia, Master Yi, Viego, Wukong, Amumu, Jarvan, Skarner. Most of these you can only contest early game and/or by landing R on them)

1. Your W2 bite does increased damage based on the enemy's missing health, you should use it as late as possible in your W frenzy most of the time if you want to squeeze out the most damage
1.1. This also applies to monsters, so smite before you W2 bite while clearing your jungle

2. Your W dash goes over terrain, both natural and champion-created, as long as the indicator reaches their end
2.1. Keep in mind that due to your initial W cast being a dash, you can NOT cast W while you are grounded

3. Your W frenzy target priority by default is attacking the closest : Champion > Monster/Minion > Other
3.1. This means if you cast W intending to attack a monster with an seen/unseen champion in range, you will reveal them and start running at them instead (unless they are invisible/stealthed)
3.2. Casting Q on anything that is NOT a champion changes target priority to attacking the closest : Monster/Minion > Champion > Other
3.3. I recommend using a keybind for the toggle of targeting champions only in your settings when you're trying to Q an enemy amidst a group of minions/monsters/etc to avoid accidentally switching target priority
3.4. This only applies to W frenzy, during the R frenzy your only target will be the champion that was hit by your R hemolith regardless of range or Q casting and you can NOT change it. If the target champion goes untargetable, you will use the W frenzy target priority until they are targetable again

4. Your E always gives 35% damage reduction for up to 1 second while you're charging it, to anything that isn't true damage and it is your main way of surviving burst and also the only way for you to cancel your W/R frenzy preemptively, always keep in mind if you have or will have it up before committing to a fight
4.1. Your E heals you for around 2.5% to 4% (depending on E's rank) max health every 0.25s during casting time, totaling to around 10% up to 16% max health heal on full 1 second cast
4.2. If you're forced under an enemy turret, E as soon you walk out of its range for the heal and damage reduction to tank the last turret shot

5. If you put an enemy into a wall using your E, slightly delay your Q until the stun from E is about to wear out to chain-CC them for maximum downtime
5.1. If you put an enemy into a wall using your E, buffering your R into them will guarantee its' hit

6. You're extremely good at stealing/securing objectives with your Smite+W2 bite burst. Keep in mind on your W2 bite cast it resets your aa and it will proc when that next aa hits, so you have to smite right before that to guarantee the steal/secure
6.1 Don't forget to Q the objective before you do this to switch target priority to monsters

7. Your Q besides enemies also lets you jump to allies and allied/enemy wards, in the latter case also dealing 1 damage
7.1. You can near-instantly kill regular 3hp stealth wards with aa-Q-aa

8. Most of the time really long range Rs are not worth it in low elo as it's a complete 50/50 if they will stand still or reactively move away as they hear it. Prioritise casting it at someone if they're within the range to not be able to react (They will hear your R sound announcement as soon as the hemolith is in flight)

9. Remember that your R frenzy gives you extra 10-20% lifesteal, 10-30% bonus movespeed (depending on R's rank) and armour plus magic resist equal to 20% of your AD while it's active, so it's more than just an infinite W and has immense value in landing, don't waste it
9.1. You can and should cast your W while you're in the R frenzy, it does NOT override it but can be used as a dash to dodge/escape key abilities and use W2 bite for extra damage and heal

I had a long phase of around a year of mainly one-tricking Briar as I was starting out League and I think she is an extremely fun, simple and consistent way of climbing in low elo, in my case from around Iron-Bronze to Gold and hitting my shortlived peak of Plat (lmao)
I just wanted to make this guide for fun as a little homage to her and the things ive learnt and experience that I've had from playing her for a while. I'm not expecting this guide to be used much but if anyone takes out something useful from it or gives Briar a try it'd be pawsome, she means a lot to me and I'm always happy to see Briar players in the wild <3