Couple things that may trip up new users.
The standard GI "swing arm assembly" AKA "J arm" that comes with your new PVS14 tends to be really tight in a variety of helmet mounts and even the issue head mount aka "skull crusher" that ships with many PVS14s.
It's not at all uncommon to have them not lock up correctly on first try, depending on the helmet mount you are using them with.
99% of the time a little "push in, pull out" action wears it in and you get good lock up.
Make sure the PVS14 is not attached to the J arm and having mounted your Rhino arm on the helmet, push the J arm in as far as it will go and then pull out. A little force (not Hulk like) will be fine. It may take a few dozen runs like this for the J arm to lock up well. This is perfectly normal. It's rare to have one not lock up correctly after a little work like this.
Personally, I've never had an issue "working it in" this way and have never had to resort to a file.
A few notes on usage-
When the PVS14 via the standard J arm is in the helmet mount assembly stowed up against the helmet mount- when you go to pull the unit down to use, you will naturally want to have your hand in the form of a letter "C" (or backwards C depending on the hand used).
Gripping this way will likely cause you to accidentally trip the release for the J arm (note on G11 mount after this).
So instead, make your hand in the form of a letter "U" when you pull down the mount. In doing so you'll be less apt to trip the release for the J arm.
On the Wilcox G11 mount, the release for the J arm is protected and this is less apt to happen, but on more common mounts like the Norotos Rhino types the release is exposed.
Good idea to always tether your PVS14. If your in a pinch this could be as simple as a piece of 550 cord or the "neck cord" from your 14 being used to tie the 14 to the helmet mount and shroud on the helmet itself (be sure to tie in a way to allow usage of device). Commercial tethers are also available on the market and a lot of folks like making their own as well.
The "Auto shutoff" issue-
This is something else that comes up regularly. The standard PVS14 housing is set up to shut off when flipped up in a helmet mount setup via the standard GI issue J arm. To a new person it sounds like an awesome feature- to be blunt, that feature sucks... It's good habit to expect it NOT to work and to get in the habit of manually shutting the unit down before flipping up.
On the PVS14 body, next to where the J arm screws in, you will notice two circular metal discs, cut a piece of electrical tape and cover these discs and the "auto shutoff" feature will never be an issue.
Aftermarket J arms-
If you decide to buy and use an aftermarket J arm- Noisefighters X14 or AX14, Wilcox, etc. Note that you can certainly expect the "auto shutoff" feature on the 14 to not work. Noisefighters does a good job of stating that upfront.
Also note that most of these aftermarket J arm are a DOVETAIL connection, which is different than the BAYONET interface on the standard GI J arm.
Just a few things I've found that tend to trip up new users. If you have any questions, post them up.