I just made a trip to Ladakh and learnt a few lessons in planning a trip. The following is meant to be a concise summary. (Disclaimer: This is based on my own experience and is by no means to be taken as comprehensive or infallible!)
Before you leave
The only mobile phone network that will work in Ladakh is the BSNL (or MTNL) Post Paid plan. So if you wish to remain connected you might want to take a post paid plan of BSNL.
The internet is very patchy at best in Ladakh and mostly non existent so it might be a good idea to inform your folks prior about your non - availability on social media and email.
High altitude sickness is a complex and ill understood disorder and is extremely likely at Leh and other areas particularly for people who are coming from sea level or relatively lesser heights (i.e. less than 2700 metres / 9000 ft). It is a good idea to talk to your doctor about taking any preventive medicines. Acetazolamide, Dexamethasone and Ibuprofen have been advocated, however these do have their own side effects, some of them as bad as having a high altitude illness. Also, if one is having a pre-existing illness, it would be a good idea to speak to your doctor.
The only sane way of arriving at Leh is by air, as the land routes from Srinagar and Manali are notorious for unanticipated closures. The security situation might also impact your travel plans. Having said that, the air route is also less predictable than other air routes thanks to the mercurial weather at Leh. It is not uncommon for the Leh flights to be diverted to Chandigarh, Srinagar or Delhi. So keep this in mind while booking flight tickets. Also check for weather predictions during your period of travel. September seems to be a safer bet than June.
The road routes are susceptible to unexpected closures, particularly the Khardungla and Changla Passes and will throw your travel to Nubra / Pangong Tso into disarray. You must talk to your tour operator about back plans and hotel reservations.
Ladakh is cold throughout the year and one would require lots of wollens / cold clothing. Be sure to add headgear and gloves. Layered clothing is more effective in keeping out cold than just a thick jacket.
During your travel
The first 24 hours after your arrival at Leh must be dedicated to complete rest and acclimatisation. A short walk at slow pace is advisable after about 8 - 12 hours of rest. One usually feels headache and inability to sleep. Take care to drink lots of fluids but avoid alcohol and smoking.
Do check the weather before embarking on the journey through Khardungla or Changla Passes. Its better to stay at your hotel in Leh than spend hours in a taxi stuck in a jam at one of the highest motorable roads in the world. Please be aware that the likelihood for acute mountain sickness is much higher at the Passes. It might be worthwhile to invest in a large oxygen cylinder and carry it in the taxi if one is traveling with senior citizens, children or others with pre-existing illness.
Ladakhis are wonderfully accommodating and friendly. However, be aware of the religious sensitivities and individual privacy while visiting monasteries, other religious places and private homes. It is customary to take off your shoes outside the main shrines (but one may keep the socks on, keeping in view the cold floor!). Photography is usually not allowed inside the monasteries. Always ask before shooting photographs particularly of women or children or of religious persons/ceremonies. Thiksey Monastery does allow photography inside some sections but it is better to ask and not to use flash or tripod. Be aware that religious functions and prayer are almost continuously going on at the monasteries and make sure that your presence or activity does not interrupt them. Needless to say, maintain sanctity of the place as one would do at any other religious place.
Street dogs are a menace, like at any other place, but more so at Leh. Avoid feeding or contact.
Hand baggage is not allowed during travel from Leh airport. Do check with your airline if they would be giving any additional free checked - in baggage allowance. Ladies bag and a laptop bag/camera bag is allowed to be carried as hand baggage but it would be better to check with your airline.
Ladakh has a strong military presence. Do not venture into restricted areas. Be careful while taking photographs as well. Photography of the Leh airport is not allowed. It is always better to ask