American English tends to use initial capitals for all content words in titles: in general terms, everything apart from grammatical items (articles, auxiliary verbs, prepositions, conjunctions, pronouns) is capitalised. British English does not capitalise in titles any more. We only use capitals for words that would obviously require capitalisation if they were in the body of the text: the first word, proper names and the pronoun 'I'. All other words are in lower case. To the British eye, capitalised titles look rather old-fashioned. I'm an editor, and I follow the British no-caps ( prose style) convention unless I'm working on a text which is specifically American English. When I work on American texts I follow the first convention, but I'll admit that I have never heard the more-than-three-letters rule. Personally, I would leave words such as 'near' in lower case, but perhaps other editors might capitalise it.

In English you in general capitalize names (Eugene, Peter etc.), names of companies (Mazda, Google), names of countries (Italy, France), school subjects (History, Arts), nationalities (Spanish, Dutch) and languages (English, German). And of course the first letter in a sentence. Why not show us your sentence, and we can tell you if it is correct? Also look at headlines online to get a feeling for what needs the capital letter.

I mean each place you publish will have its own conventions.

In English. Sorry I didn't make it clear.

It's something that varies with the publication. Where is the title going?