I wanted to point out a few errors I see all the time. These aren't writing errors so much as spelling and punctuation errors, but to a trained eye, like that of an agent or publisher, they'll leap out in an otherwise well-written page (or make a not so well-written page look even worse.)
Things About Numbers
Numbers used in text come with their own rules. The numbers one through nine are always written out in letters. Numbers ten and above are written as numerals. The exception is that when you have both, you must choose to either write them all as numerals or spell them all out. Except where it's unweildy, numbers used in dialog should be spelled out. (This doesn't apply to time, which has its own rules as well.)
When making numbers plural, as when talking about the nineties, you can write the word as I've done here, or you can use '90s. Note that there's no apostrophe between the zero and the s. That would be a possessive. It's the same with the 1990s. No apostrophe between the zero and the s.
Making Acronyms and Abbreviations Plural
I see a lot of people using an apostrophe s to make a series of capital letters plural. Actually, all you need is an s.
She learned her ABCs.
In researching this, I even found a 'grammar' site instructing people to use 's to make numerals and capital letter abbreviations plural. That grammar site is mistaken. Be careful when consulting smaller websites. For such issues consult one of the known sources of grammar information ,such as the Chicago Manual of Style or the Blue Book (grammarbook.com). If you're writing a university paper, you might be instructed to use the MLA Manual and Guide to Scholarly Publishing. These are for Americans. Wikipedia has a list of style guides for other areas of the world here.
These books are updated and revised editions are published periodically to keep up with any agreed upon changes in the rules. I check in frequently and notice that things I had become used to have been changed. Our usage evolves because new things enter the world and old usages become inconvenient or confusing.
The 'All Right' Versus 'Alright' Issue
There are grammar geeks out there who will smugly inform you that alright is not a word. Some will go on to say that it's never been a word.
Because I live on the cusp of two worlds on opposite sides of the Atlantic, I've been made to feel some confusion about this word. The British use 'alright' more commonly than Americans do and many knowledgeable people have informed me that it's not incorrect.
I've begun to allow 'alright' to stand in some British manuscripts under very particular circumstances. These are, in written dialog and in some first person narratives, where the intention is a less formal usage. I justify it with this from the Oxford English Dictionary people. I also take into consideration the fact that many Britons I've spoken to have expressed that for them 'all right' and 'alright' have different nuances of meaning. For Americans this isn't true and I don't consider it acceptable usage in American English. Neither do any of the American grammar guides.