Knowing what items to sell is the key to success. Because you can only post 10 at a time, you don't want to slow things down by posting something nobody wants.
The following is a list of items that will usually sell for 1-5fg. If you want to pinch pennies, you can start high, and each day, reduce the price until someone bites!
Arcane prefix items, especially t1. These are muteable AND glyphable.
Exp gain items, glyphable
Big Life Fish stacks, not as good as
Mana Fish stacks, your best bet!
"Useable" gear (tier III or better items with useful mods like Strength, Max Life, Enhanced Effect, Life per Kill. These are also glyphable.)
Comfreys. Mana comfreys are more valuable, and remember to suffusence them if they are tier I!
Heavies. A lot of heavies just get bought, even if they don't have cool mods. Usually tier III or higher, though.
Essences. Hard to make higher ones, but even stacks of magical tier I's can get you a few fg.Transmutation Muting useable items isn't possible without a lot of work! You need a high rank to make tier III items and higher.
You can, however, pump out a few fg making essences. Check the marketplace and undersell the competition!
Essence making is frustrating! An arcane mute can turn out to be magical. I don't recommend this skill for noobs.I bold the essence part for you.