Honestly I wonder how many people tried both and agree that it's kinda similar :D It's the part where you train yourself to ignore your instinctual reluctance and reflexes to "touch" a part of your body that's not supposed to be touched like that.

Not a contact lense wearer myself, but I think there are also soft contact lenses which might not be as hard.

I think one way to avoid the gag reflex is to "swallow" that cock. Like do the swallow motion but hold it mid-swallow (this trick works to make your Adam's apple easier to shave, too, as it kinda recedes under your skin).

Never put this theory to practice on a dick, but the gag reflex is about avoiding inhaling stuff, and we (usually) have no problem swallowing food.

When you practice with a dildo, pick one of moderate size that has an as-smooth-as-possible surface and that doesn't have an overly big knob at the end. Don't use dildos made from PVC or TPE, the material is porous and thus unsanitary, use silicone dildos instead (do clean those). And then I guess, try to relax, take it slow (really, really slow - for the beginning, try to put it in and just leave it there for a couple of seconds, instead of going straight to fucking your face) and don't overdo it. Try to practice often for a short time, rather than rarely but for a long time.

I found that it's easier (less gag-inducing) if I put the dildo on a surface and move my head onto it from the top, rather than moving the dildo with my hand while being upright or lying down. Luckily, that's a more realistic scenario for oral sex anyway!

These worked for me, hope at least one of them work for you, too!

You can start practicing just with your fingers — I find it easiest with two. Put your fingers in your mouth as far back as you can without gagging, and leave them there for a few moments, breathing through your nose. It's important that you don't go so far as to make yourself gag — I've heard that this can actually strengthen your gag reflex, so go slowly.

I found the breathing the most challenging part of it, so practicing with my fingers in this way helped a lot with that. Doing this every day made a huge difference after only a week or two. A big tip that I'd give is that you shouldn't take a big breath in before trying to deep throat — in hindsight, that's something that I would often do, and it made things harder. What actually got me started practicing this was that I saw someone who could go all the way down and basically hold a large cock in their throat for an extended time — far longer than one could do in one breath. That made me realise that I needed to focus on being able to calmly breathe through my nose at a regular rate.

If you want to move to something larger, a softer jelly dildo can be useful to practice on, I've heard, but I found that practicing with fingers was sufficient.

When you're actually going down on someone, note whether their penis has a curve to it, as many does. When I had a partner who had an upwards curve, I found that I needed to approach it from the direction of their stomach (so either lounging on the bed beside them, or straddling their chest). A downward curve makes it much easier to approach from below, which is convenient if you're kneeling and your partner is standing.

I also found it useful to actively try to relax my throat muscles. It was hard for me to know what a relaxed throat felt like at first, which meant that I found exercises like this helpful. I also found that when I was being too ambitious when practicing with a partner, my throat muscles becamenless relaxed. That's why I found it useful to practice with fingers: I had as much time as I needed to practice until things became automatic, rather than having to worry about putting on a titillating performance for a partner.

An auxiliary tip that's useful in general for blowjobs is that you can use your hands to sort of simulate deep throating by stimulating the base of the penis at the same rhythm as what your head is moving at. This also makes it easier to gradually working up to taking more of the penis in your throat, in your own time (the last thing most people want is to end up puking on their partner, after all)