1) Scope out the entity or park before "Game Day". Know where you're going to operate from. Is there an out of the way place where you can set up, or will you be right in the thick of things? Are there any prohibitions/releases/permissions needed? You want to know about these things and get them out of the way and taken care of before Activation Day. There's nothing as disheartening as showing up and having a Park Ranger come up to you and say, "You can't do this, because (insert any number of reasons) .........". And, while we're on the subject of Park Rangers ......... I know this is so basic as to almost be insulting, but I'm going to mention it anyway. No matter what else happens during your activation, PLEASE ..... at all times be cooperative, courteous and respectful to NPS employees. They're just there doing their job. It's important that we present Amateur Radio operators and Amateur Radio operations through the best lens possible. Don't ruin things for your future brother and sister Hams by being rude, pushy, or by having an attitude.
2) Know your equipment, know your antennas. Know what works, what doesn't. Take what you need (with backups), but leave the fluff at home. If you've never done a portable operations gig outside of Field Day, then you need some practice. Portable operations are not quite the same as Field Day. Close, but not quite the same. First off, your activation more than likely won't be for 24 hours, so you're going to have to consider power. Power is the most important thing. 4, 5 or 6 hours at the 100 Watt level? You're going to need to bring heavy, fully charged deep cycle batteries with you. 4, 5 or 6 hours at QRP levels? Life gets much easier. Smaller, lighter SLAs or better yet, feather-weight lithium ion batteries will serve you well.
Second, you may very well be "it". Solo ... a party of one. So that means all the work will be performed by you. Make sure your setup will be manageable by you, alone without any outside help. Don't be overly ambitious. There's nothing wrong with just tossing a wire into a tree and going "au natural". If you can manage elaborate that's all well and good, but this is supposed to be enjoyable for you, too. The KISS* principle is a good one to remember and it applies to NPOTA and portable ops in general, very, very well.
Antennas. Unfortunately, there is no "one size fits all" solution, but the idea is to make a lot of contacts. You don't want to spend all your precious time setting up aerials to get on the air, so go with antennas that are relatively easy to set up quickly. Operating stationary mobile from the car? Hamsticks, Buddisticks, Buddipoles, screwdriver antennas are all good choices. Operating away from the car? End fed wires, Buddipoles, Buddisticks, dipole antennas, and the Alex Loop are all good choices, but again, your environment (presence of trees or not?) and/or park rules will be a big factor in deciding what you can or cannot use.
Logging. Logging is one of the most important aspects of NPOTA, and you really can't be casual about it. So far, in the early moments of NPOTA, it appears as though this program is quite the huge hit. It's not unusual to tune across the HF bands and hear pileups taking place. All these NPOTA chasers want credit for their time and effort. It's your duty as an Activator, to do your best to record the QSOs as reasonably accurately as you can. Bring an accurate watch with you, preferably one that can be set up to display UTC time. For the actual task of logging, whether you bring along your laptop, or log on your cellphone (Hamlog is excellent for this!), or even log using plain ol' paper and pencil, you need to perform this task efficiently and well. Keep in mind that you will need to upload your logs to the ARRL's Logbook of the World. This is how Activators and Chasers get credit. If you're not already on LotW, then you need to send in for a password and set up an account. If you're already an LotW user, you will need to download and install the latest version of Trusted QSL. This will allow you to set up locations for your account other than "Home" using the NPOTA entity designators as location names. THIS IS IMPORTANT! If you do not upload your log using the NPOTA entity designator as your location, neither you or your chasers will get credit for all your effort. Believe me, you do not want hundreds of e-mails from angry NPOTA chasers asking you why they didn't get credit for working you. Not that that would ever, ever happen! ;-)
If your NPOTA activation will be your first solo portable experience, go to a local park away from home and try your setup there. Some people would recommend setting up in the backyard, but it's way too convenient to just walk back into the house if you've forgotten something. When you're away from home, even if it's a short distance, and you discover you have forgotten something vital, you are way more than likely to never, ever forget it again. Don't feel bad about making a checklist for yourself. Checklists are very, very good things.
3) Know yourself. Know your limits. Everyone would like to go hiking and activate that trail, or activate that park in the middle of the beauty and solitude of Nature .....but if you can't walk to the corner mailbox without getting winded - you're not going to activate a SOTA peak or a mountain trail. If you need to, find a place with a parking lot (gives you the option to operate from the car if you're not the outdoors type or if the weather is bad), picnic tables (if you're only somewhat the outdoors type) and "facilities" so your activation can be an enjoyable, exhilarating experience that you will want to repeat, and not look back upon with dread. You're most likely to enjoy your outing if you're comfortable, so dress appropriately, bring along water (and snacks if you need to), bring along some type of folding chair if you think it will be required.
4) Bring your cell phone and one of whatever VHF. UHF, VHF/UHF handheld(s) you may own. God forbid you sprain an ankle and need help, it just a call way, via telephone call or a repeater contact. The cell phone has an added benefit. If you are lucky enough to have cell service at your chosen location, you can log onto DX Summit or DX Heat and you can self spot your activation. You can quite literally go from calling CQ to pile up conditions within seconds. If you do self spot, please make sure to put "NPOTA" and your entity designator in the comments portion of the spot.
I really hope the above doesn't scare you off or deter you. It wasn't meant to, it was meant to bring some common sense ideas to be considered by new, or less experienced portable operators. Once you've left the shack and have gotten into the Great Outdoors, with your radio providing you with fun and companionship, I guarantee that you will be smitten and will want to go out and do it again, and again, and again, and again.
One last caveat. I am by no means an expert on portable ops. I'm not a SOTA Mountain Goat, nor a W1PID nor a WG0AT nor a N7UN, nor a K0JQZ for that matter. I'm just offering basic advice based upon my own limited experience. The comment box is always open, so please feel free to add to what I have written here; or correct me on anything I may have gotten wrong. We all learn when we share.
I've posted this video before, but to see how simple, easy and fun and successful this can be, here's the YouTube video that Sean Kutzko KX9X posted about his activation of Pigeon Key in Florida.