What is the proper way to distinguish between the two. I mean like does being tired effect my job performance or is it an affect?
Is there any simple rule to help out?
Well, here is a mnemonic device that might help. If you attack something, you also affect it.
If you effect something, you have merely brought it into existence. So you might effect a change, or effect a lunch out of slices of bread and cheese (the latter use is rare).
I don’t have any good uses for the noun senses: an affect is an emotional state; an effect is a result. I’ll try to find or effect some good mnemonics for these.
Nothing I write about any person or group should be applied to a larger group.
- Boris Badenov
While we’re at it, can we explain the difference between further and farther? 
“I had a feeling that in Hell there would be mushrooms.” -The Secret of Monkey Island
To answer your question, being tired might affect your job performance, but being tired will probably not effect anything at all. In fact, if you are tired enough you will not be able to effect anything except a peaceful snoring.
By the way, I thought of a mnemonic for the noun affect: an affect is like an attitude. If you are very tired, you will probably have a flat affect.
If you effect [ex- (out) + facere (to do)], you go all out to create something. If you affect [ad- (to) + facere], you just add to something already created. But there is a second ‘affect’, that means ‘to create an impression of’. The nouns spelled the same way correspond.
Ray
I’m Highjacking this thread!
Farther: More distance (like a road) Usage: “It’s two miles farther down the road”
Further: Beyond some sort of not-distance-related marker Usage: “Further study of the sample is required”
Hope it helps
Engineerboy
It’s always theE Effect. (There is a rarely used noun “affect,” but unless you’re a psycologist, you’ll never see it.)
“Affect” is by far the most common verb form and is usually the correct choice. “Effect” as a verb is only used in the sense of “to make effective.”
So use E for the noun and A for the verb and you’ll probably be correct.