How do you know which candidates to approve? Given a candidate I like, a candidate I really don't like, and a candidate I can tolerate, which ones do I approve?

Yeah, this is what makes approval not really good for normal public elections (for, say, social groups where a clear line of "approval means I commit to participating I the group activity if the chosen activity is one I approved" can be drawn, it's great.)

Basically, approval is a ranked preference ballot method that allows ties and has only two ranks. For public elections, fully-ranked ballot methods (whether allowing ties or forced-preference) are a lot more sensible; they both allow more detail in what is expressed and have more consistency in meaning across ballots in the same election.

The ones you like and tolerate - obviously!

It's not obvious, though. It's not clear whether you should mark approval for [anyone you think would do the job well] or for [anyone who you don't think would do the job badly]. Different people will read it differently, which muddies the question of whether it's accurate.

So, given Trump and Clinton who I both despise, I should not approve either and thus forfeit any say on which is better?

First of all it is strictly better than having the option to vote for only one. So you can'5 indicate your preference among the rest either.

And secondly if you start ranking then how do you combine the rankings? Do you have instant runoff? Then you have spoiler effects which THIS SYSTEM DOESNT HAVE

My point is that voting is harder under approval voting. Plurality voting is broken, but people easily understand the strategy of voting for the lesser of two evils. Under approval voting, there is no obvious strategy for deciding who should approve.

Vote for the person you would with Plurality, plus everyone you like better. That's an easy approximation.

A formal statement is here.

https://sites.google.com/a/electology.org/www/threshold

Using that strategy, it is clearly harder to vote in approval voting then in plurality. You first have to figure out how you'd vote in plurality and then do something more.

The question I was answering was: is there any way in which plurality is better then approval? Yes, it is easier to vote in plurality.

I would suggest voting for the lesser of two evils if you'd do that in a plurality voting system, plus whoever else you like better. Though there might be three equally likely winners you hate, in which case I dunno.

You can be strategic about where you draw the line. Unlike FPTP, you never have to say you're giving more support to a candidate you like less.