A Paladin that has chosen to spec Retribution is able to increase his DPS by a considerable margin. Additionally, Retribution Paladins bring a large amount of raid utility, making them valuable in endgame instances. Through the 41-point Retribution talent Crusader Strike and 51-point Divine Storm they can deal considerable DPS. In addition, Retribution Paladins are popular for their increased damage abilities for groups, such as Heart of the Crusader, which grants all attacks against the target a 3% increased chance to crit, and Sanctified Retribution, increasing the damage of the Paladin's group by 2%.
Paladins are also excellent tanks. Spiritual Attunement provides the Paladin with a percentage of mana, based on ability level, each time they receive healing. Like their Warrior brethren, they can gear to become immune to crushing blows, allowing them to tank boss level enemies. They also excel at tanking multiple mobs at the same time through use of their reactive threat abilities like Holy Shield and Consecration, an AOE effect that deals significant threat to all mobs within range. Paladins do not have as many survival tools as a Warrior tank, particularly the lack of a Shield Wall type of emergency button, and as much of their threat is reactive will not off-tank as well as a Warrior or Feral Druid. However, Paladin tanks have gained widespread acceptance in the community for their excellent threat production across multiple enemies.
The Paladin class has some of the most mana-efficient and low-threat healing spells in the game, allowing them to easily fill the position of a main tank healer in a party or raid situation. Their healing efficiency makes them great endurance and battle healers, though Paladins lack area of effect healing abilities (healing multiple targets at once) and healing over time effects can only be gained through items such as the Fel Reaver's Piston. Paladins do have a form of indirect healing from the spell Judgement of Light. However, Judgement of Light can only proc on melee attacks and does not scale with bonus healing effects, reducing its usefulness.
Paladins have several anti-Undead and Demon abilities such as Exorcism, Holy Wrath and Turn Evil which make them very effective when fighting Demon and Undead targets (not including Forsaken players, who are considered Humanoids for balance reasons).
In PvP the paladin's most well-known strength is his/her ability to outlast his opponent(s). With plate armor, their ability to heal themselves and allies, and a near-complete invulnerability every few minutes, they are a hard target to take down. Paladins can also do a surprising amount of burst-damage and have good access to stun abilities. Paladins also make great supporting characters, buffing and healing team-mates while being able to survive the enemy's attention. Paladins are particularly vulnerable to Silence and Interrupt effects, as all of a Paladin's abilities are part of a single magic school (Holy). In addition, dispel effects are powerful against a non-Retribution Paladin, as it allows the removal of the Paladin's Seal system easily.
The most important thing to remember is your strength: lasting a long time. Always keep that at the forefront and you can take on most enemies with ease.
During the early levels, you should spec retribution for higher melee damage. Use a 2-hand weapon with good dps, and wear mail armor (plate after level 40) with strength and stamina. You should also keep a shield and a fast 1-hand weapon in the bag for special situations.
When fighting, always remember to keep your aura, blessings and a seal up all the time! At this stage it is preferable for you to deal with one mob a time with your 2-hand weapon. However, when you have attracted two or more mobs, or you are low on health or mana, use a macro to switch to your shield and 1-hand fast attacking weapon and change to Seal/Judgement of Light/Wisdom. When necessary, stun your target with Hammer of Justice, or cast Divine Protection/Divine Shield. You can take this time to either run away from the danger, or heal yourself and continue the fight.
After level 30 to 40, leveling up by AOE grinding is another option. However, you need to respec to protection for this. You also need to find a fast 1-hand weapon (preferably with spell damage) and a shield and wear plate armor with intellect and stamina. Try to find an area with mainly melee mobs of similar or lower level to you. This will make the grinding much easier. See also: Paladin AoE Grinding#Where to Grind.
As a Paladin you can play any of three roles (described in greater details in the Paladin Tactics section). Paladins can DPS, tank, or heal, but which of these roles you are strongest at is based on your talent spec and the gear you bring with you. It is important to know what your role is before getting into combat and acting accordingly to prevent unnecessary party deaths and disasters.
As DPS, you'll rely mostly on procs from Seal of Command and critical hits for your damage output. With a slow, hard-hitting two-hand weapon and points in the Retribution talent tree, you can put down quite a chunk of damage, but it can be difficult to control. This means that a string a procs or crits can cause you to pull aggro off of the tank. Luckily as a plate class you can probably survive this until the tank gets the mob back; but if you're really taking a beating, you can swap in a shield in combat to increase your survivability, or use your Divine Protection or Divine Shield skill to remove aggro from yourself and back out of melee to heal. Always be prepared to help off-heal if it becomes necessary or to cleanse debuffs off of party members. A DPS paladin can also be very useful for helping the tank get aggro off of a healer, since the paladin can taunt the mobs at range using Righteous Defense and allow the tank to take them off of him without having to run across the room.
As a tank, you bring the benefit of being able to hold aggro very well on multiple Mobs and you can front load a lot of aggro quickly, allowing DPS to get into the fight early. The bad part is Paladin tanks take a bit more damage than Druid and Warrior tanks. As a Paladin you must rely on your spell damage output to hold aggro. Use Righteous Fury and do as much holy damage as you can. Try to start with Avenger's Shield (Yes, even if it's only 1 Mob!), and remember: Holy Shield should always be active while tanking. Retribution Aura can be very effective against multiple mobs, since you'll passively generate threat on each one every time it hits you. Consecration is also a great way to build aggro, but using it means you will have to be very careful about positioning so as to not break crowd controlled mobs. Keep up the buffs on your teammates - it will help the entire group in the long run.
As a healer, remember to heal the main party tank (if you are the only paladin in the group) and ensure that the focus of your party's firepower is on one mob. Make certain you continue to keep everyone buffed to the best of your ability. As a paladin, you must also switch your Auras so that they are helping your team the most under the current circumstances. Read the Paladin Tactics section for more on this. Always be prepared to jump in as an off-tank if the primary tank goes down, or if a secondary mob goes after one of your weaker groupmates. But remember that the tank is counting on you for healing, so even if you are holding off an enemy, keep healing your teammates and don't worry much about hurting the mob that is attacking you - your team will get to him as soon as they finish off the mob they are concentrating on.
The Paladin can benefit directly and indirectly from many of the professions available.
In the end, do what you want. Many of the combinations help a certain style of play and selecting a combination based on your play style will just enhance your enjoyment of the game. Remember that you can later change professions if need be. Start your professions early: they are usually inexpensive, and starting early helps ensure that anything a Paladin can create with his/her skills is applicable to the character's level. However, a recommendation for paladins are blacksmithing and mining. Blacksmithing will help you to create the best armor and certainly the best weapons, like Stormherald in the game. Mining is also good because it helps to provide items for blacksmithing. Another good choice is Herbalism and Alchemy, which provide a good source of income (Selling Herbs/Potions) and also gives you a good deal of independence, with Cooking and First Aid it lets you keep your mana for Seals/Judgement.
Cooking and First Aid are of less use to paladins than most melee classes, since paladins can heal themselves. Many cooked foods, however, do provide buffs such as a boost in total health and/or spirit. In addition, cooked foods typically sell for more than their components, providing a useful source of extra money after normal hunting. First Aid can be useful for healing when you are trying to conserve mana (or are simply out of it). Many high-level raiding groups require every character to have a high First Aid skill for those reasons. Fishing is no longer the money-maker that it once was, but can still be useful to raise your cooking skill and provide buff food.