Do Not Try to Trick the Search Engines
There are many tricks that have been tried on search engines to distort the value of a page’s content. I will not list them but you can rest assured, they have all been tried, and the search engines will penalise you for it. Just write content for your visitors and you will be fine. Never write content for search engines.
There is no hard rule for the number of words on a page. Some say at least a couple of hundred and no more than 1000, but we just get back to the rule of writing for visitors and not search engines. Write as much as is needed to create a bit of quality content.
Having said that, it is a good idea to split up very long pages into shorter pages, with titles that reflect that pages content. Again, this is good for the visitor rather than the search engine.
Keep Keywords in Mind
Each page has to have some kind of subject. You are writing about something, and that something is your Keyword or Keywords. For example, a page all about Fruit Salad would have the keys words Fruit and Salad, and perhaps even food, kitchen, health, diet etc.
Use these keywords in the title tag, description tag, keywords tag, heading and URL. See them in a way that helps the visitor decide whether or not this is the page he is looking for.
If there is an image that goes along with the content, use them in the file name and also in the alt and title tags.
Keywords help the visitor get a quick understanding of what the page is about. The more you help the visitors, the more the search engines will appreciate your efforts.
Keeping the visitor in mind, it is a good idea to highlight in bold some keyword text so that the visitor can quickly scan a page for clues as to its general content. Also use italics in the same way. Search engines like this use of highlighting text in order to help visitors scan a page. An optimised website knows what it is about and uses key words to quickly tell the reader.