I wouldn't be suprised if there is a thread for this already, so feel free to move my post if needed. Anyway, as of late i've really wanted to finally try out a Nuzlocke for the first time. I have tried to start nuzlockes in the past, but I haven't really dedicated time into playing one until now. What's the best advice for a new Nuzlocke player (i.e best way to keep track of encounters, any warnings or pitfalls from personal experience, that sort of thing). At the moment i'm planning to play through my copy of Black Version because it is one of the few games I feel okay with wiping the save data right now. Thanks in advance.

Don't stress over it. Set up rules in a way you think you'll have fun during your run. If you find out during the playthrough that you are not having fun or you forgot on something, just add/change the rules and continue on with your game. There is no need for playing by the rules you don't enjoy.

- Pokemon are more expendable than you may think in the late game -- it's the early game where one or two members dying may cost you the run.

In Emerald, by Roxanne you have 8 Pokemon.
By Wattson you have 16.
By Tate and Liza you have 46 (I might be miscounting, you may have more than that).

You can only bring 6 to the E4 *anyway*, so absolutely do not stress about completing the entire game deathless. If you're not playing with the rule where Whiting Out = Failure, you have many attempts on them, and if you are playing with that rule, then you only need 6 good Pokemon to survive that far in the first place. A loss where you take 5 deaths is not a game over. So be willing to sacrifice Pokemon that aren't very good in order to keep your heavy hitters alive. It's very common -- especially if playing with level restrictions -- that you may need to swap in a 'mon to die so you can safely swap to a mon that can outspeed and win the fight.

- Know at least the basics of competitive Pokemon. In a casual playthrough, you can power through the game on nothing but type advantage for every fight. In a Nuzlocke, you will get one starter, an abundance of water types, rock types, and aren't guaranteed anything else. You might only get one ghost type, or no fire types, or may have to rely on a team of bugs or normal types. So you often can't rely on type advantage for every gym leader. Knowing what Base Stats, IVs, EVs, and natures do, and understanding the basics of physical vs special (and remember that the split did not exist for gen 3 games) is the minimum I'd recommend people know before even attempting a Nuzlocke. You don't have to EV train pokemon at all, or calculate everyone's IVs, but it can help. I have had a run of Emerald before where against Norman, I just had a Plusle. It won. My run would have died there if I did not know how to get the most out of the little bugger.

Some more serious suggestions:
-If you're not using rare candies for leveling up, always train in areas that pose 0 threat to your Pokémon, even if it takes time. It always hurts to lose Pokémon while training.
-Crits kill more Pokémon than you'd think, so plan around them by making sure your Pokémon won't die even if the opponent crits.
-Take advantage of dupes clause by looking at what Pokémon you can get in what route before heading in. You can always use repels to skip a route momentarily and then come back late.
-Don't be afraid to sacrifice Pokémon if needed. Sometimes it's better to intentionally have one mon die so others can survive than to have that Pokémon survive at the cost of all others. Pokémon with self-destruct/explosion can be pretty useful.
-Pokémon with immunities are extremely valuable if you're playing on set mode, so make sure you use Pokémon with Levitate, Storm Drain, Flash Fire, etc.

Now, some sillier ones:
-Do not, and I repeat, do NOT mess with Koffings, Wheezings, Electrodes and the likes. Those dudes killed my Pokémon way too much with exploding moves.
-Using good, strong Pokémon is cool and all, but if you're not playing a Hardcore Nuzlocke or something of higher difficulty, always have that one Pokémon that isn't really that useful but you just want to keep it around anyways. Usually that Pokémon is your starter, because, really, you don't need to keep it on you all the time y'know.
-Have fun. Nah really. If the average nuzlocke isn't fun to you, you can change the rules to be harder or easier, like with Monotype Nuzlockes and Hardcore Nuzlockes (my personal favorite) for higher difficulty, or... Whatever kind of nuzlocke is easier than the average nuzlocke. I'm sure you can make one up, though I haven't seen many out there.

I believe nuzlockes are pretty much for everyone who has played Pokémon more than once, so as long as you're looking at the bigger picture instead of being too fixated on specifics deaths, you'll most likely have a blast.

Hi i am a pkmn trainer too so i played lots of nuzlocks reseted billions of time but i didnt lose stop trying, if you belive in yourself you can do anything,
dont stress, take breaks, sometimes it can be hard to train a low lv pokemon, but i said it one i said it twice belive in yourself.