Flying between countries is an airport process: signposted, staffed, and broadly the same everywhere. Crossing on land is a completely different activity, and it is where a lot of otherwise well-planned trips lose a day or an unnecessary amount of money.
Almost all of the friction is predictable.
Before you go
Check the crossing is open to your nationality. Not every border post issues visas, and not every post accepts every passport. Some are for locals only. This information is on your foreign ministry’s site and on recent traveller forums, and it changes.
Check whether the visa is available on arrival at that specific post. A country may grant visa-on-arrival at its international airports and not at a remote land crossing. This is one of the most common ways people get turned back.
Have the documents ready before you queue: passport, a pen of your own, passport photos (two, more often than you expect), the exact fee in the currency they want — frequently clean US dollars — proof of onward travel, and an address in the country for the arrival form.
Photograph everything and keep copies offline.
Money at the border
Bring the fee in cash, in the right currency, in good condition. Border posts do not take cards. US dollars are the default at many crossings and torn or pre-2009 notes are routinely refused.
Do not change your remaining money with the men at the border unless you have to. Their rates are poor and short-changing is common. Change a small amount to get you to the first town and use an ATM there.
Know the real exchange rate before you arrive, on your phone, offline.
The unofficial fee
At some crossings you will be asked for a payment that is not on any published schedule — a “processing fee”, a “stamp fee”, a “health form”.
Some of these are genuine and locally set. Some are not. The approach that works: ask politely for a receipt. A genuine fee has one. A request for a receipt frequently makes an invented fee evaporate.
If it does not, the sum is usually small, and a lengthy principled stand at an isolated border with a bus waiting is a poor use of your afternoon. Judge it in the moment; be polite throughout; never lose your temper with someone who controls a stamp.
Fixers
At most busy land crossings, someone will attach themselves to you offering to speed things up. Some are official, some are useful, most are neither.
You do not need one. The process is: exit stamp on one side, walk, entry form and stamp on the other. Following the crowd works.
If you do use one, agree the price first and do not hand over your passport.
Timing
Cross early in the day. Border posts have opening hours, close for lunch in some countries, and onward transport thins out sharply in the afternoon. Arriving at a border at 4pm risks being stranded in a border town, which is rarely anybody’s favourite kind of town.
Allow far more time than the distance suggests. Two to four hours is normal for a busy crossing. Some — Cambodia to Vietnam, Zambia to Zimbabwe, several African posts — take longer.
Avoid national holidays on either side, and the days around them.
Buses that cross
Two models, and knowing which you are on matters.
Through buses handle the crossing collectively: the driver collects passports, everyone gets off, forms are processed together. Convenient, and the bus will wait — though not indefinitely.
Change-at-the-border means your ticket ends on one side and you walk across and find onward transport. Cheaper, more common on short routes, and it is where people end up stuck.
Ask which one you have bought before you buy it.
The scams that recur
The fake border office — a shed before the real one, taking a “fee”. The real post has a flag, a barrier and uniformed officials.
The visa mark-up — an agent offering to obtain your visa-on-arrival for a fee, standing next to the counter where you can get it yourself.
The onward-ticket trap — being told you cannot enter without one, by someone who happens to sell them.
The insurance requirement — occasionally genuine for vehicles, frequently not for people.
Vehicles
If you are driving your own or a rental across:
The rental company must authorise it in advance, in writing, and will charge for it. Many exclude specific countries entirely.
A carnet de passage is required for taking your own vehicle into a number of countries and is arranged months ahead through a motoring organisation.
Third-party insurance valid in the destination country, often bought at the border.
No fresh food, meat, dairy or plants, particularly on the Chile–Argentina crossings, where inspection is thorough and fines are real.
After the stamp
Check it. Wrong dates, wrong duration and missing stamps happen, and they are your problem when you leave. A missing entry stamp can mean being treated as an illegal entrant on exit.
Count the days you have been given rather than the days you asked for.