Black dragons have amongst the highest defence for a normal monster in RuneScape - their melee defence is quite high, so using melee against them is not advisable. Despite this, they are weak to ranged attacks, and are most vulnerable to crossbow bolts.
They attack with a Fire Bolt spell that usually damages in the low 300s, as well as a long-distance dragonbreath attack. As with all dragons, an anti-dragon shield, a dragonfire shield, super antifire potion or Protect from Magic prayer are essential when fighting them, although it is possible for higher levels to get by using only Soul split. Without one of these forms of protection, players can be hit extremely hard by dragonfire (over 2000 points of damage). Lower-leveled players could potentially be killed in one hit by this attack. However, when using one of the listed protections, a player will be hit for much less. (Praying against magic reduces the average damage to about 250, as well as weakening their main magic attack.) An anti-fire potion used in addition to the shield will reduce the damage dealt by the breath to just one point. Additionally, players with a Herblore level of 85 may use a super antifire potion which negates the dragon's breath without the need of an anti-dragon shield or protection prayers, allowing players to safely use a two-handed weapon or dual-wield weapons with less need for prayer.
The dragon's melee attacks are only used if the player is in melee range. Thus, if ranging or maging, it is advisable to stay out of the reach of their melee attack. These monsters are primarily weak to bolts, which allows use of an Anti-dragon shield for relatively safe kills with a one-handed crossbow. However, if you wish to attain the fastest kill rates (through dual wielded or 2-handed crossbows), you will need Protect from Magic or Super antifire potions.
As of the Evolution of Combat update, black dragons are magic based creatures, which gives a considerable penalty to melee accuracy. Because of this and their extremely high defence, at least chaotic weaponry is required for a consistent kill rate, and even then is not recommended unless there is no other alternative.
Note: Always use Turmoil, Piety,Chivalry or the Incredible Reflexes and Ultimate Strength prayers. These dragons have extremely high melee defence and a good amount of health, boosting your offence is a must if you wish to obtain a worthwhile kill rate. A good amount of overloads is also recommended for a higher damage output.
Ranged is by far the most effective way of slaying black dragons. The best setup would include the usage of two-handed or dual wielded ranged weapons and super antifires. If one does not have access to super antifires, regular antifires / protect from magic / deflect magic are viable options but then you will need to bring along food. If using dual wielded weapons, it is a good idea to use Needle Strike before using more powerful attacks such as Snipe or Snap-Shot.
Notes: If you do not own a void set (deflector optional) and you are killing these off-task, you can use the on-task gear to replace it, but void will lead to faster kills, especially if using a strong crossbow. You can range black dragons without antifire measures if you are very careful, by using a weapon with a large attack range, such as the Royal crossbow. You can also bring an antifire shield to use only when running out of your safespot to pick up drops. Remember, at least three pieces of Void knight equipment must be worn along with the Void ranger helm to receive the set effect. With the addition of the Void knight deflector, players could swap out one of the pieces (other than the helm) for other equipment, but this disallows the ability to dual wield and still requires super antifires, so is not recommended. Note: It is highly recommended to use prayers like Eagle Eye and Rigour to speed up kills, as well as (extreme) ranging potions. If using these prayers however, it is advisable to keep an eye on your prayer points, especially if using a bow without super antifires. If your prayer drops and you don't have other dragonfire protection, the dragonbreath can deal large (and potentially fatal) amounts of damage.
Using magic against black dragons is quite effective. With the use of 2-handed weapons, Protect from Magic, Deflect Magic, antifire potions, or super antifire potions are needed.
It is recommended to stay within melee distance if a player has high defence, is using full ganodermic or if a player is using only one protection method, doing this will make the dragon attack less with dragonfire.