There are no general rules as such.
To get toned muscular arm u need to focus on what u are doing. Set your self a goal. If u want to have a muscular arms then concentrate on reps and sets and weight u are using.
To begin with try
Beginner level
4 sets with dumbbells
1st set 4 kg 10 rep
2nd set 4 kg 10 rep
3rd set 4 kg 10 rep
4th set 4 kg 10 rep
once u get the technique and posture right ,We advance into next level
Intermediate level
4 sets with dumbbells
1st set 4 kg 10 rep
2nd set 6 kg 10 rep
3rd set 8 kg 10 rep
4th set 10 kg 10 rep
do this until u have attained the final objective of 10
kg 10 rep
advance level
2 sets with dumbbells warm up level to get that blood flowing into your vains
1st set 4 kg 15 rep
2nd set 6 kg 15 rep
3rd set would be your best weight, with which u can do 10 rep
4th set would be slightly heavy to challenge your self for your personnel best of 10 reps with next heavy weight.
Make sure u rest in between sets for about 90 sec, Proper breathing technique posture, positives ( when u are lifting up ) and negative ( when u are bringing your weight down ), make sure you are not cheating while lifting.
If u can log your proress using excel sheet on a day to day basics and compare it with your weight recorded on daily basis u can analyse how things have improved and u may want to push it more further