When faced with a long tail keyword phrase use proper grammar for your site. Long-tails can be misspellings but that is not how you want to be found. This does not mean you can't play around a little with the keyword order if it makes sense when you read it. You want to attract clients who can tell the difference in your products. You want to capture the attention as quickly as possible.  A trick that might be palatable is to reference the correct grammar and in a non judgmental way against the incorrect grammar. ' Some people call our 'widget'', a "widgette", or "widgetes" however the proper reference is "widget".

Unless  your site is just designed to bring in any traffic for something like AdSense advertising then content (and proper grammar) go out the door.

The less traffic the better on the long tail. It just has to have some primary keyword(s) in it.

For instance I will take Google Analytics, go to "traffic sources", select keywords, then within the report I sort by the lowest traffic which brings up the long tail keywords. That is I'm building on something that already exists and to my eye makes 'sense'. Now I know the technique with the spreadsheet and all that and it can be useful but you are creating keywords that in my mind are unqualified. Highly recommended if one has no place to start but as your sites get traffic you should be able to pull out real long tails and build on those. Having a mix is great, just using the spreadsheet method is not so great (unless you are building off some real long tails).What the long tail in this case is trying to 'answer' is

'medical device product development process'

let's say my primary is 'medical device' of course that is kind of broad even for a medical equipment manufacturer. I'm not going to get a whole lot of qualified traffic with that.

long tails:

medical device product

medical device product development

product development process: medical device

development process: medical device product

Where you put them in your copy really depends on what you are trying to achieve.  The 'real' long tail in this example is 'what is the medical device product development process?"

'Real' long tails are searches that the SE has a hard time fitting into the 2 and 3 word keyword phrases (which a long tail really is not)

We are trying to answer the question (and in the process restate the question)in the page content we are optimizing for.

I may or may not rank for 'medical device' and I don't care because (we assume) I'm really after other combos that convert and do not fall into the broad search gorge.

having some of the long tail in the URL is OK. More important is the anchor text, page title, h1 tag and copy.