Given the fact that most writing these days is typed, you don’t need to dot your i’s and cross your t’s, but you still need to pay attention to mechanics, including the following items:
Spelling: A good spellchecker catches most typos, but it may not catch the use of wrong words, such as their instead of there and its (possessive of it) instead of it’s (short for it is). You still need to proofread your prose and know how to spell and use a dictionary.
Capitalization: Capitalization is a convention that helps readers identify names, titles, headings, beginnings of sentences, and so on.
Punctuation: Knowing when to use periods, colons, semicolons, commas, dashes, quotation marks, and so on is essential to cueing your readers on when to pause and to helping them move through your writing smoothly.
Abbreviations: Abbreviations, including e.g. (for example), i.e. (that is), and etc. (etcetera), serve as a form of shorthand. Conventions for forming and using abbreviations ensure that readers know what each abbreviation stands for.
Numbers: Conventions regarding numbers cover everything from whether to use a comma to mark the thousands place to whether you use numerals or words for 1 (one) to 10 (ten).