Buses are usually the quickest and easiest form of transport between Nepal and India. A trickle of travellers enter Nepal at the Mahendrenagar-Banbassa border crossing in the extreme west of Nepal, which is handy for travellers coming overland from Delhi who do not want to visit Varanasi. The crossing between Nepal and Tibet via Kodari is open to organised groups but not to individual travellers heading north. Be prepared with alternative plans if you're thinking about using this route, because landslides regularly make it impassable during the monsoon. It's advisable to book domestic flights a week in advance and keep re-confirming your ticket just to make sure you don't slip off the passenger list if the flight is full.
Airlines only accept payment in hard currency from visitors.
Kathmandu's domestic airport is a shabby, chaotic place usually full of stressed tourists whose flights have been delayed. Public buses are the main form of transportation and are incredibly cheap, incredibly uncomfortable and tediously slow. There are several services between Kathmandu and Pokhara aimed specifically at tourists. Those who dislike having chickens and goats supplementing their human travelling companions will prefer them. There are no trains and no drive-yourself rental cars in Nepal.