This topic is simple. Avoid the use of slang. Technical jargon is one thing, but sloppy slang is never acceptable. Some words, such as cool, have made their way into accepted language. Words ending with –izzle have not. Any use of words like ain’t, yo, dude and homie is unprofessional.
Save it for the water cooler, or better yet, the weekend.
This rule goes double for foul, sexist or racist language. It’s not only unpleasant, it could get you fired. If you’re unsure about a phrase, it’s probably best avoided.
The words you write are a direct reflection of you. You wouldn’t walk into the office in dirty, wrinkled clothes…don’t let your writing leave the same bad impression.
Resources
In addition to a good dictionary and thesaurus, there are numerous style guides available. The can be useful when you're confused about the use of a word, as opposed to its meaning. Popular and widely accepted guides are The Chicago Manual of Style and Strunk and White's.