Double progression
Set a range, say 10 to 15 for lateral raises or 8 to 12 for curls. Stay at the same weight, adding reps week to week until you reach the top of the range on all sets, then bump the load and reset to the bottom of the range.
Use double progression, add reps within a range first, then add a small load and drop back to the bottom.
Accessories rarely progress by adding weight every session like a squat does. Use double progression, pick a rep range such as 8 to 12, add reps each week until you hit 12 on all sets, then increase the weight by the smallest jump and start again at 8. Keep every set within 0 to 3 reps of failure so the lighter loads still drive the smaller muscles.
Set a range, say 10 to 15 for lateral raises or 8 to 12 for curls. Stay at the same weight, adding reps week to week until you reach the top of the range on all sets, then bump the load and reset to the bottom of the range.
Small muscles cannot handle a 5 kg leap on a curl. Use 1 to 2.5 kg increases, or add a rep instead. If your gym lacks small plates, use fractional plates or simply chase more reps and cleaner tempo before adding weight.
Accessories still need to be close to failure to grow. Because the loads are light, take these sets within 0 to 2 reps of failure and control the eccentric rather than swinging, so the target muscle does the work.
Use double progression, add reps within a range first, then add a small load and drop back to the bottom.