watch demos

Sticky traps are very flexible depending on the situation and will vary quite often. The best sticky traps are in obscure locations that the other team will not expect.
To test out, just walk around on a server with a friend and try out different spots for being out of sight and damage. Otherwise, just watch high level demos and watch where they put their stickies.

Im just gonna leave a small chapter of my book here

Ultra key of power: to make sure you dont overextend yourself as a demo to setup some fancy ass trap that either
-wont work and will get you killed
-dont overextend to watch the trap if you know they have uber ad in particular, num ad is extremely situational and I cant explain it
-a trap that will work at the cost of your life (not worth unless miraculous combo drop or multi kill, prolly not worth it either but extremely situational)

watching demos of invite demos is literally the best way to learn new sticky trap spots
-literally learned a new trap watching a i46 platinum demo raping my team leader like last week lol
-pay attention to what traps work (down below, deserved own post cause its so important)
-for ex: you'd be surprised how effective a simple 3-4 sticky carpet is, that too on a floor that everyone can see

another important thing is to always have a read on the situation, this will allow you to access whether traps should be used or damage output

going back to what traps work, there are times when you as a demo should set carpets or traps to control area, other times you can get kills if you catch onto enemy push patterns, helping you know where to trap, I like to mix it up, you dont wanna keep trapping the same shit over and over again lol, any fucking demo will mix it up, in this case, matches, scrims and pugs are your best friend to teach you these small things and experience will hone your timings and understanding

remember that the goal for every trap shouldn't necessarily be to get a 3k combo drop, something that forces them to clear or pop through early is still good depending on the situation. delaying them by 5 seconds could allow you to get your own uber or respawns

you can learn traps by playing against other demos, and after a bit you'll get better at spotting your own spots

If enemy team going to push soon and you need to delay push/force pop - put stickies on floor where everyone can see

If you want pick because its stalemate situation- put trap (usually on flank position, combo expects it) in hidden spot where a player could extend to during their push. Dont overextend for this but if your team supports you, you can bait yourself to kill players with traps like this (bdonski is very good at doing this).

To expand on the watch demos thing. Watch muma, his traps at i58 were amazing. Also every time a demo places a trap pause the demo and for a few seconds think "what is the uber/player situation? what is he trying to accomplish with this trap?" Etc

The thing about sticky traps is that people know there's always going to be one and they will always check the traditional spots. You can still use this to delay the enemy team, as was covered by others above, but if you want to frag then you're going to need to use your brain.

You will notice patterns the more games you play. You will notice that over time people will go through some specific routes more often than other specific routes. Whilst everyone expects a sticky trap in a chokepoint or in a traditional old spot, they will not expect it in a place that is more remote. I'm not saying you should put traps in any random spot and gamble, but instead to observe patterns in scout/solly/demo/medic routes and put your stickies where they are likely to go.

For example: In badlands, when the enemy team is pushing into your second, they may inspect choke and expect a trap waiting for them at the point, but few are those that check the bush leading up to ramp. Even though they are not forced to walk over the bush (whereas they are forced to go through choke and go on the point), it is habit for many players to do so anyway.

So instead of mimicking other people's most likely very outdated sticky traps (like the example I gave lol), you would do better to follow the line of thought here presented and adapt to the game. This will prove itself a valuable tool and keep you in the game even when the enemy has figured all your novel sticky traps out.

Also take into consideration that all traps do not have to be used to kill. You can also use your traps to force the enemy team into a certain direction, or area, that is less convenient for their well being.

Pretty much every general idea has been mentioned here, except that I barely see any demos putting down traps as a bait for your other trap. you can force people into a certain direction or area to make them easier to spam, bomb, etc., like sigh said, but you can use that to your own advantage as well--to bait them into walking on your other trap. Generally you would only do this when you're trying to get a pick and potentially give your team a chance to push or repush, not when you're trying to force their team. In that case, having traps in as many places as possible is usually most ideal.

i literally just wanted a video. Anyone?

#11 if you actually read everyones (really good I might add) replies you would figure out that not only is there not really a video of this but why there isn't

https://www.youtube.com/watch?v=7HfVdMIMAKQ
old video but slin goes into detail about why and where traps are placed throughout the video,

A good demoman never reveals his best sticky traps

I saw a really smart one where the guy put a few stickies where they could easily be seen, and then when the enemy ran in, saw the stickies and instinctively backed up quickly, they stepped back into the real trap and he det.

I can't remember who did it. It was some guy pugging and chatting shit over the top of it. But I remember thinking it was a smart idea. Tbh I can't even think what map it was on. A great help, I know.

Set up a trap, back up, start setting another trap when you know they can see you setting it. Watch first trap.