The best way is getting her wet and ready, then size and roughness, and finally anal.
From this picture you can see that the clitoral nerves aren't just in the front (the little hammer-shaped part), but extend deep inside wrapping around her vaginal canal and behind it. This means there's a huge mass of clitoral nerve endings that you can hit when you're entering through her ass. Thickness compresses these nerves more and makes them easier to stimulate, but jumping in before she's ready doesn't work. Interestingly, fear has the same physiological effect as arousal, so I trick I use (especially the first time I meet a woman) is to take advantage of the fact that I'm a somewhat scary-looking brown man to make her nervous and afraid. I'm a nice and open guy when we talk online so she knows I'm safe to meet but the first time in person is always a little different and I'm told I come off as intimidating (as long as I don't smile or laugh). I used to resent this (racism), but I finally found the upside of it, which is that she's a bit aroused because we already talked about what we're going to do but here's this strange dark guy looking at her, putting his hands on her and touching her neck and hair, and she starts to feel a little afraid... and really wet.
From there on, it's about keeping her a little scared - treating her roughly and pushing her around (or slapping her suddenly if she mouths off), and fucking her a harder than she is used to, making her feel like it's a little out of control. Telling her beforehand that you'll be using all of her holes means she isn't surprised to feel you lubing up her back door, and the combination of trust, excitement, fear, and anticipation all build up so that if she hasn't cum already, she definitely will when you're finally inside her ass. One girl who told me she'd always needed clitoral stimulation to cum in the past literally came the
moment I entered her ass for the first time - I'd bent her over a pillow to make it easier, applied some lotion (we were young and didn't have real lube), and she just screamed and started convulsing as soon as I was in.