Choose a starter who is good defensively and handles many of the gyms well. you'll kick yourself if you lose a starter because it's weak to an early gym-leader.
Use a nuzlocke tracker such as THIS one to keep track of your Pokemon
Only apply the rules of the nuzlocke after receiving pokeballs
Apply the dupes clause and family clause, which mean that if you find a Pokemon that you already have, or one that's from a family you already have, it doesn't count as the first of the route
PUT THE TEXT SPEED ON FAST
If you want it to be brutal, put your battle style to set and never use items in battle. if you don't want it to be too hard, then just don't.
Have a plan for every gym, and underestimate no one.
Don't take unnecessary risks
If you catch a Pokemon that you'll never use, keep it as a sacrificial pawn for when you need a free switch-in in a tricky battle
Instead of releasing Pokemon when they die, have a graveyard box in your PC
Sell any revives you find
Look up where and when you'll be attacked by rivals in advance
Heal at every opportunity
Don't be afraid to grind
Don't use legendaries
Don't count gifts as your encounter for the route, but refuse them if they're too broken (Like Latios and Mega lucario)
when replacing a team member, consider type diversity
if you play a game with single-use TMs, consider how likely a Pokemon is to die if you use a TM on it