What is the fastest way to level up my speech skill?

How can I level up my speech skill? Does selling items and persuading people increase my speech skill? Does it increase my speech skill when I wear fortify speechcraft and haggling clothes and drink fortify haggling potions?

This has been patched and is no longer possible.

There is also a glitch that you can use to get speech up to max really fast:

Summary for those who can't watch the video: Go into the Black-Briar Meadery in Riften (after 8:00am, when it opens) and talk to the guy working there. Ask him about Maven, choose the "(Persuade)" option, repeat. (You might need to bribe him the first few times to get your Speech high enough to have a Persuade option.)

Does it increase my speech skill when I wear fortify speechcraft and haggling clothes and drink fortify haggling potions?

These are skill modifiers. They provide an increased speech skill while working, but do not raise your speech skill or provide skill experience.

How can I level up my speech skill? Does selling items and persuade people to tell the truth increase my speech skill?

You can persuade people, but the opportunities to do so are few and far between.

You can also find a speech trainer to convert gold directly into skill levels. This gets expensive above skill 50.

Instead, the fastest way is to interact with a merchant. Both buying and selling provide speech experience. The amount of gold determines this amount. Selling 5 items for 20 gold each or 1 item for 100 gold grant the same skill experience.

If you just buy and sell the same item back and forth to a merchant, you'll rack up a bunch of skill experience while only losing a portion of the item's value in the process. You could also combine this with other skills... Buy ingredients, craft a potion, sell it. Buy materials, make a weapon, enchant it, sell it. The more money that changes hands, the more speech skill you will gain.

I found it very effective to try and steal from guards, then persuade them to overlook it. They will let you go once. Every guard will let you go exactly once, the second time around that exact guard will not look the other way, but instead he will arrest you.

The fastest way is to barter i.e sell stuff to merchants. Persuading people also increases your speech skill, but it is easier to increase it by selling items since finding people to "convince" is more time-consuming.

Good luck!