It all looks so splendid, and the authors assume that the spell check and the grammar check will make things immaculate.
First use a spell check on your computer and then proofread a printed out version.
Making a common mistake such as not using the correct version of there, their or they're will not be caught by spell check.
Once you've finished your document, be sure to spell check for simple misspellings and typos.
Be sure to run a spell check program as well.