Spotting techniques are about seeing the damn thing, not knowing what it is. Now I have an ulterior resource, danger sense, which alerts me to hazards before I recognize them, and often leaves me hunting around for the hazard before I find the inch-high poison ivy plants mowed short with the lawn. I can't teach you that. I can tell you how I scan an area. I realized that nobody seems to have written down this part of the process, just the identification tips. So here's what to do ...
* When you go outside, sweep wide first. Identify areas where plants come near a trail or otherwise where you might go. Look for the kind of habitat that poison ivy particularly likes. Sometimes it creeps along the ground or forms a bush, but it most loves growing along fences, up trees, or other supportive and protective structures. It's also a bandage plant, meaning it gravitates to disturbed soil.
* Teach your attention to snag on anything with three leaves, and avoid it unless you can identify it as definitely harmless (e.g. wild strawberry). It is better to avoid a harmless plant than to touch a toxic one.
* These steps often spot poison ivy if it is present. Finding it in its favorite places lets you know it's there, so you can look for it in other places. Disturbed areas may have it all over everywhere. Healthy forest tends to have it scattered around.
* Look before you move. Keep sweeping your attention in smaller arcs as you go through an area, focusing on mid-range and short-range spaces ahead and to the sides of you. Poison ivy can be small and it hides in shadows or cracks. When you spot it, call it out to other people with you. Once is enough if they are alert. Otherwise you may need to point out every bit of it.
* Remember every part of the plant is dangerous and a light touch is enough to get it on you. Even in winter, the bare stems can be hazardous. Don't grab unidentified plants or move carelessly through wilderness. Make sure you know what you're putting into a campfire too: smoke from poison ivy is also toxic.
* The oil can transfer from other people or objects to you. Never drag objects through the brush without first examining the trail you plan to take. Don't let other people crash around and then hug you or throw their clothes on your sleeping bag. If the oil gets on a chair or carpet, it can be all but impossible to remove effectively, and from there it can get all over the house. Take off everyone's outdoor clothes over a tiled floor if possible, which is easy to clean. Possibly contaminated clothes should be washed twice, the first time in hot water with extra detergent, and don't wash anything else with them.
* Wash thoroughly with soap and water if you think you may have come into contact with poison ivy. Most people have a few hours before it affects them. The worse your allergy, the less time you have to remove a contact poison and escape the consequences. The less allergic you are, the longer you have. Remember, that timer starts ticking down from when you touch the plant, not when you leave the woods or get home. If you spend all day in the woods, you can be itching by the time you even get back to your car. While most people day a few days for the rash to come up, some can show welts within hours, and very few people who are allergic at all have a full day to get the oil off in time. Factor that into your trip timing if you normally go into ivy-infested areas.
The most important part of this process is learning to recognize that three-leaved pattern while scanning an area. It's also the easiest to practice. If you have a park that's mostly clear but with weedy edges, that's a good place to practice. That's the kind of way I learned. If you don't have a ready source of poison ivy, have a friend make 3-leaved dummies from construction paper or similiar-looking leaves from silk plants such as poinsettia, and hide them for you to find. You want to get to where you run those steps without thinking about them much, and it works like an emergency brake. When the skill is fully mature, your lizard brain will stop you before you've consciously noticed why, and at that level it does work a lot like my danger sense. The difference is the poison ivy must be visible to you -- you won't alert to it behind you or under a box like I have sometimes. So if you're outside and suddenly find yourself stopping, look around your feet and overhead to figure out why before you move and maybe touch something you shouldn't.
If you know that you will be going into an area full of poison ivy, you can apply ivy block products in advance and then dress in clothing that covers as much of you as possible. It's useful for the middle of the bell curve who are moderately allergic. However, that doesn't protect people who are so allergic that a speck is enough to make them itch. Just avoid areas with a lot of poison ivy.
If you are seriously allergic to poison ivy and you go in the wilderness, either you learn to take care or you will get a rash. Other people will call you paranoid. Ignore them. They aren't the ones who'll be itching for days or going to a doctor if you get careless. You are. Listening to people bitch for a few hours is less miserable than getting a rash. Also, if people don't respect your self-care routines, next time try to go out with people who aren't assholes.
For those of you with the "not allergic to poison ivy" superpower, please don't be a dick about it to naries without it. Some people are very vulnerable and it can cause more than a trivial rash. Respect their self-care routine, whether that's walking mindfully or avoiding forests. Don't grab them if you're not equally careful, because you might have the oil on you and it spreads. You can help by scouting for poison ivy. The more allergic someone is, the more likely they'll appreciate extra eyes on the oograah.