If you're planning to head to Acadia National Park, the Great Smoky Mountains or any of America's inspiring national parks in 2016, you're in luck. With the National Park Service's centennial fast approaching this August, this is the year to embrace quality time in the great outdoors without paying an entrance fee. Best of all, you don't have to wait until August 25 to 28 to enjoy pass-free visits or take advantage of fun recreational activities and ranger-led programs. In honor of this year's milestone, visitors can enjoy fee-free entry to all 58 national parks April 16 to 24.With that said, there are some caveats. For one thing, while the centennial isn't until August, "the tourism crush has already started," says Jason Cochran, editor-in-chief of Frommers.com. "The vendors who manage lodging options within park boundaries, particularly in the American West in parks such as Yosemite and Yellowstone, are reporting sold-out rooms through the summer peak travel season," Cochran says. "If you want to stay inside a park and you haven't booked it now, you'd better look as soon as possible, although you're probably already out of luck for this summer," he adds. And beyond the demand for accommodations, you'll contend with high crowds given the uptick in demand this year. But never fret: To help you navigate these enchanting parks like a pro, we caught up with national park experts to bring you top hacks for planning a hassle-free trip. [See: Best Adventure Vacations in the USA.]If You've Procrastinated, Rely on a Reputable Outfitter"Reservations are absolutely essential," says Everett Potter, a columnist for USA Today and author of "Everett Potter's Travel Report," emphasizing that often hotels in popular destinations like Yellowstone are booked up to a year in advance. Even mom-and-pop motels and smaller inns are going to be very busy this summer, so it's best to make your plans as soon as possible to ensure availability, he cautions. If you haven't locked in your plans, another great option is a biking or hiking trip with a trusted tour company, which will have access to rooms. Potter points to the travel company Backroads as an ideal choice for multisport trips to popular parks such as Yellowstone and Yosemite. The outfitter offers multisport hiking and mountain biking adventures in major parks across the country, including Zion National Park, geared toward a variety of traveler types and activity levels."If you don't feel comfortable hiking or camping, there are tour operators you can use," says Salwa Jabado, senior editor, Countryside and Adventure Travel, at Fodor's Travel, pointing to Backroads and REI Adventures, which will "set you up with camping gear and the whole nine yards," she adds. REI Adventures, which offers three- to 12-day trips with expert-led tours everywhere from the Grand Canyon to Death Valley National Park, has varied activity options to cater to diverse age groups and preferred activities, from climbing to backpacking.Stay in Off-the-Beaten-Path Spots and Pick Off-Peak Travel TimesWhether you want to plan a family-friendly adventure, discover a tucked away national treasure or explore on your own, there are plenty of parks to pique your interest. But it's important to remember that if your sights are set on a family camping trip this summer, all lodging options – even campsites – are filling up quickly. "Look instead at the shoulder seasons, which are spring and fall when the kids are in school," Cochran says. And if you have less flexibility in your schedule, consider lesser-visited spots near park entrances, he adds, such as Jackson Hole, Wyoming, near Yellowstone and Mariposa, California, near Yosemite. "You'll find overflow motels and hotels there, and the prices tend to be much lower than at the major in-park resorts, anyway," he says. "Don't be put off by the drive into the park because the land is nearly as beautiful outside the park as it is inside, and you'll also have more options for food if you stay outside the boundaries," he adds. The only drawback to staying outside a park is finding parking, Cochran cautions. He advises checking out the NPS.gov website in advance of your trip, since regulations vary depending on the park. "More parks, such as Muir Woods National Monument north of San Francisco, where you'll find those gorgeous redwood trees, recently instituted parking restrictions that force many guests to park far away and take a shuttle into the forest," he explains. And this trend is sweeping across the country, he adds. Beyond heavy parking restrictions, securing an ideal spot near the park entrance during the peak season can be tricky. [See: 6 Family-Friendly Adventure Trips You Can Afford.]Pack Prudently to Ensure Safety and Comfort "You always want to protect yourself from the sun and the cold," Jabado says. She advises bringing along a daypack with essential items such as a sunhat, sunscreen, a reusable water bottle and high-energy bars. And since national parks urge visitors to bring their own food, it's a smart idea to bring a picnic, with food to grill and a cooler, she adds. While many parks do offer food services, transportation and shops (there are 500 NPS concession services across 120 different parks), it's a great idea to pack along items such as nuts, dried fruit, protein bars or sandwiches in a cooler that will not spoil or draw attention from animals. And when it comes to luggage, she suggests carrying a backpack or duffel and leaving the clamshell suitcase at home. "Carry twice as much water as you think you'll need," Cochran says, emphasizing that it's easy to lose moisture while hiking. And if you decide to go off the beaten path, sign in at a ranger's office, he says. That way, they'll know if you don't return on schedule. "And don't touch anything – you don't want to be like Vanessa Hudgens, who's in trouble for posting an Instagram of what looks like carved graffiti on a rock in Sedona [Arizona]," he adds. Also keep in mind that some high-demand and challenging trails can require registration in advance for safety purposes, so check NPS.gov ahead of your visit, Cochran says. Consider All OptionsSince popular national parks such as Yosemite and Yellowstone fill up six to 12 months ahead of the peak summer season, it's also advantageous to look for lodging outside of major parks and map out day trips, Jabado says. "If you can be flexible, you're certainly going to have more opportunity to stay at an RV or a camping spot," she says, highlighting that the majority of camp sites are available online through Reserve America, a company that handles reservations for the Park Service. And if you have some flexibility, along with searching for campgrounds nearby the park you're interested in, consider a midweek trip to optimize availably, Jabado adds, pointing out that "you don't have to spend 100 percent of your time at the park." First, scope out the park visitors center to learn about ranger-led hikes, talks and other happenings, then enjoy a few memorable experiences outside the park. For example, if you want to check out Utah's pristine parks, like Zion or Bryce Canyon, you could carve out a day to enjoy white water rafting in Moab, she says.Go Early to Beat the Crowds and Capture Great ShotsIf you want to dodge crowds this summer, your best bet is arriving early before thousands of visitors descend upon popular areas. "Try to go during the golden hours," Jabado says. Around sunrise and sunset, the "photos are just going to be magnificent," she adds. As for photo composition, for the best shots, remember the rule of thirds, and ensure top elements are along the imaginary grid lines when you split your picture into thirds, Jabado says. It's also better to avoid using zoom features on your smartphone for clearer, crisper shots, she adds. And if you decide to bring your camera, don't forget to pack along a small tripod for getting sharply focused, steady shots, Jabado says. [See: 15 Must-Visit National Park Attractions.]Explore Lesser-Known ParksIf you don't want to battle crowds this summer, go to off-the-grid national parks that everyone in your group will enjoy. "There aren't many national parks in the continental U.S. that I wouldn't recommend for families," Cochran says. Thanks to versatile trails, which are ideal for easy, moderate and advanced levels, as well as the parks' interpretive centers and expert-led tours, it's easy to find a park that's right for you and your companions. "Do yourself a favor and research," Potter says, pointing out that there are plenty of quieter parks that don't get nearly as many visitors at top-visited destinations like Yellowstone and Acadia National Park. He suggests considering parks in remote destinations like Alaska, as well as under-the-radar but nonetheless scenic and exciting outdoor destinations such as Black Canyon of the Gunnison in Colorado and Isle Royale National Park in Michigan."There are a ton of places that are underrated," Jabado says, recalling a visit to Dry Tortugas National Park, just 70 miles west of Key West, that offers a historic fort, snorkeling opportunities thanks to its striking coral reefs and ranger-led tours. To help you narrow down your options, Fodor's has put together a National Parks Finder that allows users to pinpoint a park that meets their ideal activities, region and season.