1. Visit Grammar Girl Daily
This is a free website with daily tips on grammar rules that we should be using everyday. From how to use "effect" and "affect" correctly to when to use a comma, you can learn it from Grammar Girl.
2. Don't rely on spell check.
We will never become better spellers if we continuous use spell check without trying to spell the word ourselves correctly. I have really been trying to figure out the spelling of a word before asking the computer to do it for. If you still can't spell it on your own then of course use spell check. No parent wants a newsletter full of mistakes from their child's teacher.
3. Use prepositions correctly.
It is easy to forget what a preposition is when it isn't in the course you teach. It is even more difficult to remember how to correctly use them. However, using prepositions correctly can make your writing sound much better.
Quick Tip: The main rule you need to know is that prepositions go in front of a noun, not a verb.
For example, in the sentence "We rode to the mall for lunch.," to the mall is the prepositional phrase, with to being the preposition. To is before a noun, not a verb. Click here for a list of prepositions.
4. Changing Y to I
If you are adding a suffix like -ness then you change the "y" to an "i" and then add the suffix, like in the word happiness. However, if the suffix you are using starts with an i then you leave on the y, like in the word carrying. I've often see people want to throw away the "y" before adding -ing, so make sure you remember leave the "y" alone.