The capitalization of a title is largely a stylistic choice; however, the major style guides do make certain recommendations.
Chicago Manual of Style:
The Chicago Manual of Style states that the first and last word of a title should be capitalized in addition to
• a few conjunctions, and
• subordinating conjunctions.
Prepositions are capitalized if they are used in the context of an adjective or an adverb.
Associated Press Style:
According to AP style, you should capitalize the first and last word of a title in addition to all principal words and all words longer than three letters. Principal words would essentially be the same parts of speech listed above.
You can choose to write your title the same way that you would write a sentence. This means that you would capitalize the first word, proper names, and any other word that would normally be capitalized in a sentence.
A General Rule:
The key is to be consistent in how you capitalize titles throughout your document, publication, or website. You also do not want to be too informal, which is often the case with online publications. For example, you should avoid the temptation to capitalize every word or to make every word lowercase. You also should not capitalize every letter of the title. This can be difficult to read and even come across as shouting.
Dealing with Company Names:
Certain company names, such as iPhone or eBay, can pose a sticky situation when used at the beginning of a title. The styles guides advise that the first word of a title should be capitalized, but that does not agree with the company’s branding. The best course of action is to simply rewrite the title to avoid using the company name at the beginning.