There are many things you can put on it; honey, mollassess, corn syrup, anything sweet & sticky really. They even make flavored grease/waxy stuff for bits.
It's up to you if you want to use it the first few times, just to get a good impression but it's not absolutely necessary
I've only sweetened up a bit like that for a horse that was spoiled or sour, but had already been there. Mostly as a trick to make them take the bit and buy me time to get the headstall on and start the whole "it's not a bad thing" process.
For introducing the bit, honey or molasses or something along those lines isn't necessary. As long as you can get the bit in their mouth without a BIG fight, you don't need to trick them into it.
I am on the shorter side and sometimes have a hard time reaching up to fit the headstall over her ears. She knows this and when the mood fits she uses it to her advantage. If it's safe to use and is a common thing it might be a nice distraction while trying to put something new in her mouth.
Just as a side note - make sure that you have her teeth done BEFORE putting a bit in her mouth. If her teeth are not adequately floated, the bit can cause pain for her and you will find yourself struggling big time to convince her that a bit isn't so bad.