Delhi-Leh flights operate daily. Flights are very reliable in summer, while in winter they are sometimes cancelled in case of heavy snowfall. There are 8 flights per day in each direction. Flight tickets can become very expensive during the peak season. All airlines are equivalent (Air India, GoFirst, SpiceJet, Vistara, IndiGo) so you may select the cheapest ticket that you can find.
If you opt to come or leave Ladakh by road, you can take either the Manali or Srinagar Highway. The roads are closed in winter and they usually open in May. The 2-day road trip can be done by bus or by taxi.
Leh is at 3500m above sea level so acclimatization can get difficult because of high altitude. It is advisable to spend at least two days to acclimatize before you set out for your adventures. Drink plenty of water or other fluids such as soup, tea and juice.