I’m not sure if I please my girlfriend when giving her oral sex as she’s never had an orgasm from it. What are your tips for satisfying her in this way?

The best person to answer that is your girlfriend! Don’t be shy about asking her to let you know (through sighs and groans if not words) what she likes and doesn't like. Try different speeds and pressure of lick. Generally women like little flicky licks of the tongue, although some like more lapping licks, or swirls, even small sucks. The left side of the clitoris is often more sensitive. Try adding vaginal or anal stimulation with your fingers or a vibrator for added sensation. The most important thing though is simply to keep on going! It can take quite a while for a woman to orgasm, so settle in and keep the attention constant and regular. Let her relax into it so she can completely receive without any thought other than the pure pleasure she’s experiencing (or running her favourite fantasy through her head, which could well tip her over into orgasm).