Most fantasy novels that I've read aren't set entirely in jungles; they give the heroes a place to poke around after that interesting lost statue of Krackakawak or something. But even as minor settings, they can be done better than they are.
1) Realize how alive the jungle is. It's not a forest. There are insects everywhere, birds everywhere, vines and trees and flowers everywhere. (Which can cause problems; more on that in a moment). You're not necessarily going to see every animal that makes a sound, but you're not going to go through long stretches of silence, either. If silence does start spreading, there's almost certainly a large predator nearby whose attention the smaller animals don't want to attract. However, even a tiger calming down one part of the jungle in passing won't do anything for the other parts. They'll go on whistling, shrieking, screeching, bellowing, buzzing, howling, spitting, and swaying.
Heroes used to forests have a right to be unnerved by the jungle (not that they ever are). A character might walk a whole day through a forest without ever seeing more than the occasional bird and squirrel, especially if he isn't trained in observation and the animals are shy of hunters. There shouldn't be that absence of life in a jungle. Holes in fantasy ecosystems are bad all over the place, but plug them with extra care here.
2) Moving through a jungle is hellishly hard work. Unless a fire has just come through and cleared away a good number of the trees, there will be plants in the way at every step. Lianas and other vines that hang from trees can smack unwary adventurers in the face. Vines straggling over the ground can trip them. Undergrowth bunching together can prevent getting through at all without the aid of a machete or similar instrument. Tree roots, unexpected little bumps in the ground, and animals crouching still in the hopes of avoiding detection all make walking over the jungle floor a far cry from trotting through one's living room.
The problem comes when fantasy authors make it as easy to walk in the jungle as in a living room. Apparently someone comes through and hacks cleared roads every now and again, or the heroes are following a "trade route"- even if the path to wherever they're going has been lost for hundreds of years.
Before giving your jungle-inexperienced heroes free license to pass wherever they please, ask yourself why someone would keep the road open. Do the worshippers of the god whose temple they're seeking really welcome visitors? If yes, there might be a clear green path they tend regularly. If not, it doesn't make sense for your heroes not to spend a lot of time hacking and grunting and sweating.
3) The jungle grows enormously quickly. There's a reason that tales of "lost cities" in the rain forests convince people. The jungle is like the ocean or the desert in this sense; it can swallow human habitations with no sign that they've ever been there. Unless your heroes are lucky enough to stumble on the temples or walls or whatever by accident, they're unlikely to find a place that was abandoned even just a few years before.
Fantasy authors sometimes try to get around this by having the heroes memorize landmarks that don't change. The problem comes when those landmarks, like bare hills, are just as likely to get overgrown, or when the heroes have no way to get above the jungle and see the lay of the land. Even stone obelisks can be toppled by vines growing around them and pulling them down. If the trees and the vines eat the landmarks as well, the heroes deserve to be stumbling around, saved only by luck.
If you're going to have your heroes find their way back to an ancestral home, choose a landmark that can neither be toppled easily nor lost in wave after wave of green, or you're going to have, in Rudyard Kipling's words, "the roaring jungle in full blast on the spot that had been under plough not six months before," and the heroes saying, "Huh?"
4) The jungle is hot. Yes, another obvious truth, and one that fantasy authors don't deal well enough with. The sun isn't the only thing that makes the jungle so hot, either; it's incredibly humid most of the time, in the way that a desert isn't, and that means that even people who are prepared for heat are going to have problems that they won't in a desert.
For one thing, the exertion of getting through a jungle, whether it's hacking through vines or just the sheer walking, will make your characters sweat. However, they can't wear light clothing if they don't want to get eaten alive by the hundreds of insects that are also present. So they have to wear heavy clothes and sweat under them. That's not going to make them feel, or smell, very good.
For another, the air is hard to breathe, especially if your characters are mountain-dwellers or desert-dwellers and accustomed to air that's considerably thinner. It can feel as though you're being smothered with a wet blanket if you aren't used to it. And meanwhile, you have to keep walking, and sweating. There isn't an escape from it, the way that there is in the mountains if one simply heads downhill.
And finally, the pace of rotting in the jungle is intense. Put something in the ground, and the plants and the heat attack it, reducing it to its component parts as soon as possible and making it part of the soil. Heroes who bury food to come back to later aren't going to have any food to come back to, unless they put it in a box made of metal. Bodies of characters who die are going to have to be buried or burned immediately. If they're left as they are, the heat will start rotting and liquefying them within a week. Leather, cloth, and other materials that are not metal or stone have the same problems. Even metal can start rusting if it's left wet.
Don't make things easy on your heroes, especially if they come from less humid environments. There's all sorts of adventure potential in making it hard.
5) The seasons are not the same. If your characters are traveling during the non-rainy season, they should be subjected to crippling heat and have problems finding water. The water holes and rivers they do find will be smaller than normal, and are likely to have attracted wildlife. Nothing like stooping over a pond to get a drink and suddenly finding yourself the target of an irritated python.
If it's during the rainy season, the heroes should have a whole other set of problems. Rain in the jungle is often heavy, near-constant, hard to keep out of clothes or supplies, and likely to flood rivers and lowlands. The characters are unlikely to find shelter beneath trees, since the leaves can tip out their loads of water easily and soak them. If they take shelter in valleys, they have to watch out for runaway rivers. If they are following a cleared path, animals may be using it as an escape route, or water may turn it into mud.
I've never seen fantasy characters caught in a rainstorm in a jungle and battered and wet and hungry to within an inch of their lives, but it would be fun.
6) Remember to describe the jungle. It's probably the most colorful habitat in the fantasy world, and authors who have a lot of purple prose issues to work out couldn't ask for a better subject. Unless it's a drought, flowers are everywhere, and full of different hue on hue. Parrots, poison-dart frogs, and birds of paradise may inhabit your jungles, and none of them are drab. Neither are some of the monkeys and langurs, or the tigers and leopards and ocelots and jaguars.
One thing that always disappoints me is when a fantasy author who can find endless variations of green to describe in a forest is somehow not up to tackling the more obvious palette of the jungle. If you're not sure what kind of jungle environment you want, or what kinds of animals and flowers are most common, for the gods' sakes go research them.
For good, realistic descriptions of jungles in fantasy, read Glen Cook's Black Company series, which uses Indian and Vietnamese mythology and settings, or the Monarchies of God series by Paul Kearney, which features an alternate world where the characters are just starting to explore their version of America. Best description of the heat, insects, and jungle-traveling problems I've ever read.