The first and most important guideline to jungle trekking is not to go alone and ensure you bring with you a very dependable Garmin GPS with extra batteries.
Most parks have rangers that will go with you for anywhere from free to 500 baht and they are usually a wealth of information and provide safety (depending on the park some will even carry guns and give instructions in the case of animals etc).
I would suggest staying on trails that are listed in the park maps(this site is a wealth of information on great trails), animal made trails on the edges of parks are often confusing and it can very well lead you to be lost quite quickly.
As for the animals, if your on trails long enough you will eventually run into them. Here are a few things I would say or suggest:
-I carry a USA made bear spray which they say is good for 20 meters distance (havent had to use it yet)
-If you see Elephants on trail, immediately turn and walk away from them. It seems the ones who stick around for a photo shot or an opportunity for a better look often can lead to issues. Look for options for going up or downhill during your exit. Also remember that when an elephant walks, its feet make little or no sound, mostly what your listening for is the movement of brush/trees
-For bears, same applies as above, walk away at a relative pace(not running), usually they wont be interested in you or will run away from you
-For guar, well seems you wont have a ton of time to react as they seem to be so stealthy until alarmed and heard a few stories of broken ribs from a startled guar hit and run
-For snakes, its best to have high boots if possible along with long pants (leech socks as well). This will also keep out the ticks and leeches which are often frequently found on park trails. Although I have never seen one, I have heard mother cobras are quite protective when on their leaf nest, dont stick around these if you see or hear them obviously.
I am sure I have missed a few things the other members can chime in on
Getting lost is often more an issue than the 'dangerous' animals you might encounter, so Jonathan's advice is wise, even though I don't always stick to it myself.
I love exploring new areas, wildlife tracks but honestly I believe chances to see wildlife on established tracks are higher. Often there is less leaf litter on the official trails. So you walk much more quietly.
When you hike Off trail elephants or bears will likely hear you coming before you notice them.
If you do go on your own, make sure somebody knows more or less where you are going. And a GPS will ensure that you know where you are going. As backup bring a compass.
Keep your distance is indeed the best advice. I have followed Jonathan's advice and picked up pepperspray on a night market. For sure not the quality Jonathan is talking about, but well, it makes my wife feel more comfortable when I carry it. And I guess it would help if you get actually attacked by a bear.
Watch where you step or which branch you grab. Even though I consider the green tree vipers as not aggressive, they will certainly bite when you grab them by accident. And so will a snake you step on. But I think the chances are very slim. But if you are unlucky and on your own, then it will likely end up extremely bad for you... Recently somebody posted a link to a webpage explaining what to do in such an event, very useful information that could save your life!
Other than that, just be careful, use common sense, and enjoy!
Unbelievable how relaxed this man remains during this charge. I have had my own close encounter (not this close, but still way too close and I happened to be cornered) but it took me a while to get over the enormous adrenaline rush. I was certainly not as cool as him!
During the whole video the elephant has his ears pointed at the man. It did not exactly come as a surprise.
Though, I do get the feeling that this was not the first time this man has encountered wild elephants.
I guess that 9 out of 10 times standing your ground would work, but I see no need for doing so. The elephant wants you to get out of his comfort-zone, so by running away you give him space. It is not a tiger or other predator, for which running could trigger their predatory instincts.
Elephants are very dangerous, but I think conflict is usually easy to avoid. I think bears are the most fearsome mammals in these jungles. Even though from my experience they tend to not care about your presence, or move away, still I believe they could just as well be fearless and go after you. Not sure if standing your ground would help. Climbing a tree won't either... Still I feel safer in the Thai jungles than on a Thai highway.