Google has strict editorial requirements for text ads. These restrictions in general are there to foster an environment of fair play between all advertisers and help consumers find relevant information. Here are some guidelines which you need to follow to get your ad approved:
Accurate ad text: Your ad must reflect what the consumer will find on your landing page (e.g., your ad talks about yoga mats and if that item is not on your landing page or on your Web site, then Google can fall back on this rule if they want to disapprove your ad copy).
Accurate Capitalization: You can capitalize the first letter of each individual word; however, you cannot capitalize an entire word with some exceptions (e.g., FREE Yoga Class will be disapproved since the word FREE is capitalized. However, Free GRE or GMAT Class would be acceptable as these are acronyms).
Proper Spelling and Grammar: You cannot have misspellings in your ad copy (e.g., Luv instead of Love). However, alternate spellings are acceptable (e.g., color and colour).
Unsubstantiated Claims: Unsubstantiated claims are not allowed. For example, you can not use superlatives such as "the best coffee in the world" in your ad copy unless such claims are substantiated with proof available on your Web site. Also, if you quote a price or special offer, then you must show the same to the consumer on the landing page or a few clicks from your landing page.
Formatting and Punctuation: Your ad copy can have only one exclamation point and that exclamation point cannot be in your headline. You cannot repeat the same word multiple times in the same row (e.g., Free Free Free, will not be allowed).
Miscellaneous: Your ad text cannot contain any offensive or inappropriate language. You can not imply a Google affiliation or relationship that does not exist.
At the high-level, Google also provides the overview of its AdWords policy in the screenshot below. (Source: the image below is directly from Google's AdWords support center)