The following addons are recommended. These are not definitive, as there are many addons that are similar to the ones listed below.
Lets face it, classic WoW is a grindy game. Unlike retail where you get XP for doing any type of profession, classic you do not. So picking flowers, and mining, will not get you xp. They do help with making money. To circumvent this, you need a profession that requires you to be killing mobs to get XP. The following are professions recommended to help leveling. - In short it is any profession that requires you to grind mobs. The following profession will allow you to kill mobs and get xp to help with the grind
Using this tip, you will not be able to use the associated profession (example if you get skinning, you need to get tailoring as well – so you can grind on all types of mobs to get mats and XP).
This again, is optional, but have found that if you need to grind for XP, might as well work on professions at the same time! Level efficiently! And make some GOLD!! Remember in classic/vanilla you need to be constantly earning XP as at higher levels, quests are not as abundant.
Another reason for this, is because, many people do not like doing dungeons, but instead, just explore and gradually level up. Because of this, they will lack the XP that the dungeon players get. When going out of your way to work on professions that give you XP, you will be ahead in the levels, and can bypass the dungeons if you prefer.