You probably already use some of the strategies discussed below. Experiment with different tactics until you find a system that works well for you. The important thing is to make the process systematic and focused so that you catch as many errors as possible in the least amount of time.
Don't rely entirely on spelling checkers. These can be useful tools but they are far from foolproof. Spell checkers have a limited dictionary, so some words that show up as misspelled may just not be in their memory. In addition, spell checkers will not catch misspellings that form another valid word. For example, if you type "your" instead of "you're," "to" instead of "too," or "there" instead of "their," the spell checker won't catch the error.
Grammar checkers can be even more problematic. These programs work with a limited number of rules, so they can't identify every error and often make mistakes. They also fail to give thorough explanations to help you understand why a sentence should be revised. You may want to use a grammar checker to help you identify potential run-on sentences or too frequent use of the passive voice, but you need to be able to evaluate the feedback it provides.
Proofread for only one kind of error at a time. If you try to identify and revise too many things at once, you risk losing focus, and your proofreading will be less effective. It's easier to catch grammar errors if you aren't checking punctuation and spelling at the same time. In addition, some of the techniques that work well for spotting one kind of mistake won't catch others.
Read slow, and read every word. Try reading out loud, which forces you to say each word and also lets you hear how the words sound together. When you read silently or too quickly you may skip over errors or make unconscious corrections.
Separate the text into individual sentences. This is another technique to help you to read every sentence carefully. Simply press the return key after every period so that every line begins a new sentence. Then read each sentence separately, looking for grammar, punctuation, or spelling errors. If you're working with a printed copy, try using an opaque object like a ruler or a piece of paper to isolate the line you're working on.
Circle every punctuation mark. This forces you to look at each one. As you circle, ask yourself if the punctuation is correct.
Read the paper backwards. This technique is helpful for checking spelling. Start with the last word on the last page and work your way back to the beginning, reading each word separately. Because content, punctuation, and grammar won't make any sense, your focus will be entirely on the spelling of each word. You can also read backwards sentence by sentence to check grammar; this will help you avoid becoming distracted by content issues.
Proofreading is a learning process. You're not just looking for errors that you recognize; you're also learning to recognize and correct new errors. This is where handbooks and dictionaries come in. Keep the ones you find helpful close at hand as you proofread.
Ignorance may be bliss, but it won't make you a better proofreader. You'll often find things that don't seem quite right to you, but you're not quite sure what's wrong either. A word looks like it might be misspelled, but the spell checker didn't catch it. You think you need a comma between two words, but you're not sure why. Should you use "that" instead of "which"? If you're not sure about something, look it up.
The proofreading process becomes more efficient as you develop and practice a systematic strategy. You'll learn to identify the specific areas of your own writing that need careful attention, and knowing that you have a sound method for finding errors will help you to focus more on developing your ideas while drafting the paper.
Check out this fun site - http://pages.prodigy.net/pizzabagel/MisspelledSigns_001.htm
There are 30 pages or so of misspelled signs! Actual signs from businesses.