You know what they say about experience being a hard teacher - she gives the test first and the lesson afterwards.

There is no substitute for hands-on knowledge. Kudos for giving it a try, sounds like you learned a couple of lessons there. Don't be too hard on yourself though - and don't give up the concept of the poncho shelter just yet. To be fair, I think your expectations of the military poncho lean-to may have been a little unrealistic.

The good old poncho lean-to does work well for what it is, and within its own set of limitations. You will find it depicted in just about any survival manual (for a good reason I suppose) even though of late it seems to be getting a little less popular.

For all its limitations, the poncho lean-to happens to be the type of shelter that I use most of the time. I've spent a good number of (surprisingly comfortable) nights under one. From the Highlands of Scotland where it kept me dry from an endless downpour, to the open desert, the Alps in wintertime (with snow cover and well below freezing) to temperate woodland, which is my primary environment.

To make it work properly though, you have to keep in mind that the poncho lean-to is not a complete shelter per se. It only achieves two things when constructed properly: it will keep you dry and (mostly) protected from wind. With improper construction and placement though your lean-to is likely to fail even at those two basic aims.

Not all ponchos are created equal. My go-to model is a cheap German army poncho made of some kind of stury OD synthetic fabric (vinyl IIRC). I've used it for almost 15 years and it's still going strong. It's long enough to keep me fully under cover, and I'm 6'2". In a pinch it could even accomodate two people as long as you don't mind huddling together. If you look around and try different models I'm sure you could find a surplus or civilian poncho that would suit your needs.

Your poncho is nothing more than a roof. Whether you opt for a simple single-sloped lean-to or a double-pitched A-frame - do make sure you pick a good spot sheltered from the wind. Preferably in a small hollow or natural depression, with your back to a large log or boulder, etc. Place the entrance away/perpendicular to the prevailing wind direction.

In cold weather extra ground insulation is a must. Even in a pine forest the existing layer of needles compacted on the ground is generally inadequate to guarantee a good night's rest. Make a bough bed if at all possible. If unavailable, look for dry grass, leaves and moss. In any case, strive to create a springy raised matress to get your body at least 3 to 4 inches above ground level.

A simple double-pitched lean-to is not the best choice in cold, windy and/or rainy weather because it's open on two ends. If no better option is at hand you can make your shelter much warmer by lowering the back end of the shelter as far toward the ground as practical. You can further enclose it with a backpack if you carry one, it will also make a decent makeshift pillow.

If the conditions are really horrible you could opt for some other type of shelter entirely, such as a debris hut and use the poncho only for the outer layer to keep you dry. And don't forget that fire will make all the difference. Ideally facing the entrance of your shelter, with a reflective screen behind if possible.