How to approach price negotiations on 2nd hand car?

[newcar]

I'm visiting my car dealer this week to have a second look at a car I want to buy (my first) and would like to see if I can get a deal on the price.
Dealer did say last time that the price is pretty much the lowest he can go so not holding up for much, however he could just be saying this.
Also I've done my research and the price does seem reasonable in comparison to other cars of the same make/age etc.
But I still want to try however! Does anyone have any advice on how to approach this? Is it worth putting the ball in his court to ask if he could offer me a discount or should I put my offer on the table first?
I'm clueless about these things.
I'll be paying cash if this would help in my favour?

I've found that you just can't haggle prices down as much as you used to be able to. I remember buying my first couple of cars coming away feeling I'd done a good deal after playing the game, now they just seem more reasonably priced and it's all a lot more transparent.

Cash won't help as it costs them money to bank it, our local dealer prefers debit cards as it doesn't cost him.