Arms are a secondary muscle group that are often thrown in at the end of a primary muscle group such as chest or back days. The most common practice these days seems to be to train the secondary mover with the primary, for example chest with tris and back with bis. this in theory works well for for a blood volume/pump style of training that is focused more on conditioning/shape but as for size and strength a different approach may be more effective.
Training these in an opposite way will be far more effective for building size and strength as the secondary muscle group isn’t pre fatigued at all and is able to perform practically at maximal capacity just as if you trained it by itself.
Being able to move more weight for more reps (given the reps are of good quality) will in time result in a bigger and much stronger muscle. The only problem to training with this method is that it may be difficult to implement it into your current split and you need at least a day between the two workouts but two would be advised.
Keeping in mind that delts should be avoided before chest and rear delts should be avoided before or after back its best to split these up by throwing a leg session in between these muscle groups to break it up and let your muscles completely recover.
So now that the structure is taken care of exercise selection should be the next point of interest. i recommend three exercises for tris and the same for bis. varying the angles and the strength curve as much as possible to target the maximal amount of muscle fibres. a mixture between cables, dumbbells, barbells and machines is the best way to ensure this is done correctly.
Changing your grip up between supine, neutral and pronated will also enable you to target different areas of the muscle more effectively. generally speaking the more your palm is supernated the more bicep muscle fibres are activated as this is when your bicep is at its shortest position.
If your arms are truly something you’re wanting to bring up then training them on their own seperate day cannot be beaten in terms of size and strength gains but this often comes at the price of sacrificing training frequency for back and chest so think carefully before considering this option.