Subject - Verb agreement?

You would use the plural verb when you are talking directly about the object, so "Spectacles help me to see better", but use the singular verb when you refer to them as a pair, because 'pair' is singular.

You cannot write "A spectacles" because 'spectacles' is a plural word. You would either say "a pair of spectacles is on the table" or "some spectacles are on the table".

Technically, "Two scissors" is also incorrect though it sounds more passable because "two" requires a plural anyway, but it should be "Two pairs of scissors are in the drawer."

"Spectacles" is never singular, so "Spectacles are on the table," not "A spectacles." "Spectacles help me see better."

"Two scissors are in the drawer" is fine. One pair of scissors is "these scissors." I have heard some people use "a scissors," but not anyone I know. It may be a regional thing.

This says "scissors" can take both a singular and plural verb:

http://dictionary.reference.com/browse/scissors

i could bypass with A vase of plant life grew to become into located in the table. My clarification is right here: the area of the sentence is vase, "of plant life" is a characteristic of the vase.

Nouns that are always plural (trousers, glasses, scissors, etc) still have to be treated as plural even when there's only one of them.

For example:

Spectacles help me see better.
My glasses are on the table.

You can't say "a spectacles" either, as the article still needs to be plural. You could try instead:
"some spectacles", or "someone's spectacles" are on the table.

"Two pairs of scissors are in the drawer" makes sense, but even if it was singular you still treat it as plural: "There are some scissors in the drawer".

Hope this makes sense =)