Figure: MID/ASIA Region, from Eddie's notes.
Regional differences from the ICAO standard can be found in ICAO Document 7030 and your Jeppesen Airway Manual. Both of the sources, however, can be out of date. See International Operations Manual / Regional Introduction for ideas about getting up-to-date information.
As countries around the world update navigation systems and procedures, it becomes increasingly important to speak with somebody who has been to the airport recently or have a contact in country with local knowledge. As we say in the military, there is no substitute for boots on the ground.
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.
This region is moving from a mix of navigation requirements to the system of Performance Based Navigation outlined in ICAO Document 9613. Current navigation requirements are available on Jeppesen Airway Manual Air Traffic Control pages and Chapter 4 of each region covered by ICAO Document 7030.
[ICAO Doc 7030 Amendment 1, §MID/ASIA, ¶22.214.171.124.]
This requirement was due December 2013 but has slipped.
More about this: International Operations / Required Navigation Performance 4.
[ICAO Doc 7030 Amendment 1, §MID/ASIA, ¶126.96.36.199.3.1.] Within the Amman, Baghdad, Bahrain, Beirut, Cairo, Damascus, Jeddah, Kabul, Kuwait, Muscat, Sana'a, Tehran, Tel Aviv and Emirates FIRs, only RNAV-equipped aircraft having a navigation accuracy meeting RNP 5 may plan for operations under IFR on those ATS routes and within those level bands which have been specified as requiring RNP 5 in the relevant State AIP or NOTAM.
[ICAO Doc 7030 Amendment 1, §MID/ASIA, ¶188.8.131.52.] For flights on designated controlled oceanic routes or areas within the Auckland Oceanic, Brisbane, Fukuoka, Ho Chi Minh, Hong Kong, Honiara, Kuala Limpur, Melbourne, Nauru, New Zealand and Port Moresby, Sanya and Singapore FIRs, a lateral separation minimum of 93 km (50 NM) may be applied.
[ICAO Doc 7030 Amendment 1, §MID/ASIA, ¶184.108.40.206.2] For flights on designated controlled oceanic routes or areas within the Auckland Oceanic, Brisbane, Fukuoka, Ho Chi Minh, Hong Kong, Honiara, Kuala Limpur, Melbourne, Nauru, New Zealand and Port Moresby, Sanya and Singapore FIRs, a longitudinal separation minimum of 93 km (50 NM) derived by RNAV may be applied between RNAV-equipped aircraft approved to RNP 10 or better, in accordance with the provisions of the PANS-ATM, 220.127.116.11.
Keep in mind RNP 10 is an exception to the rule of Required Navigation Performance standards, "RNAV 10" retains the "RNP 10" designation for matters of convenience.
[ICAO Doc 7030 Amendment 1, §MID/ASIA, ¶18.104.22.168.1.1.] For flights on controlled oceanic routes across the Tasman Sea within the Auckland Oceanic, Brisbane, Melbourne and New Zealand FIRs and for flights across the South China Sea within Bangkok, Hanoi, Ho Chi Minh, Hong Kong, Kota Kinabalu, Kuala Lumpur, Manila, Taipei and Singapore FIRs, the minimum lateral separation shall be 110 km (60 NM).
Not all countries are WGS-84 compliant. For two examples of many:
More about this: International Operations / World Geodetic System 84 (WGS-84).
[ICAO Document 7030, Section MID/ASIA, Paragraph 4.2.1] RVSM shall be applicable in that volume of airspace between FL 290 and FL 410 inclusive in the following FIRs: Amman, Auckland Oceanic, Bahrain, Bangkok, Beijing, Beirut, Brisbane, Cairo, Chennai, Colombo, Damascus, Delhi, Dhaka, Emirates, Fukuoka, Guangzhou, Hanoi, Ho Chi Minh, Hong Kong, Honiara, Incheon, Jakarta, Jeddah, Karachi, Kathmandu, Kolkata, Kota Kinabalu, Kuala Lumpur, Kunming, Kuwait, Lahore, Lanzhou, Male, Manila, Melbourne, Mumbai, Muscat, Nauru, New Zealand, Phnom Penh, Port Moresby, Sana'a, Sanya, Shanghai, Shenyang, Singapore, Taibei, Tehran, Ujung Pandang, Urumqi, Vientiane, Wuhan and Yangon.
[Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures, China, 11 Oct 2013] China RVSM has instituted Metric RVSM in the Shenyang, Beijing, Shanghai, Guangzhou, Kunming, Wuhan, Lanzhou, Urumqi FIRs between 8,900m (FL291) and 12,500m (FL411). ATC will issue the Flight Level clearance in meters. However due to the rounding differences, the metric readout of the onboard avionics will not necessarily correspond to the cleared Flight Level in meters. Use of the China RVSM FLAS Diagram to determine the corresponding flight level in feet is required to ensure a minimum of 1000' separation. The aircraft shall be flown using the flight level in FEET.
More about about this: Procedures & Techniques / Reduced Vertical Separation Minimum (RVSM).
There is a broad cross section of QNH, QFE, and hybrid mixtures of the two. You will need to check the Jeppesen Airway Manual Air Traffic Control pages for each country to be sure. Here is just a sampling:
[Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures, China, 11 Oct 2013]
More about this: International Operations / Altimetry, Metric, QFE/QNH.
Some countries use non-standard transition altitude and transition level procedures. For example:
[Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures, Far East, Singapore, 20 Dec 2013] A common transition altitude of 11,000 ft (3350 meters) has been established in the Singapore Flight Information Region. This will ensure uniformity in the transition altitudes for aerodromes within the territories of Brunei, Malaysia and Singapore, except for an area of radius 10 nautical miles centered on Mount Kinabalu where the lowest safe altitude will be 15,000 ft (4,570 meters) and the lowest usable flight level will be FL170.
More about this: International Operations / Transition Altitude / Layer / Level.
[ICAO Document 7030, Section MID/ASIA, Paragraph 6.4.1]
Note.— PACOTS guidelines containing detailed information on track generation, lateral track spacing, level assignment, position-reporting requirements and other relevant details shall be published in the AIPs or associated supplements of those States which utilize a flexible track system within their airspace or areas of responsibility.
Each country departs in some ways with the ICAO standard and common US practices. Pilots should always refer to the Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures pages for each country on their itineraries for differences with ICAO Standards, Recommended Practices and Procedures. More about this: International Operations / US versus ICAO.
The following are a sampling of some of the differences, there are many more. You should check the Jeppesen Airway Manual State pages for every country you takeoff, overfly, or land.
Some countries in the Middle East / Asia region modify or publish an exception to ICAO Approach Ban procedures, prohibiting takeoff, continuing en route, starting an approach, or continuing an approach if the destination weather is below minimums. You need to know the rule for your destination before takeoff. More about this: International Operations / Approach Ban.
Middle East and Asia lost communications standards tend to be ICAO Doc 4444 compliant. That should alert all U.S. pilots that they are different from what is used in the United States.
More about this: Abnormal Procedures / Lost Communications.
Some countries employ Strategic Lateral Offset Procedures (SLOP) over domestic airspace. For example:
More about this: International Operations / Strategic Lateral Offset Procedure (SLOP).
Some countries have uncontrolled IFR airspace requiring a "listening watch" procedure on air traffic advisory service frequencies. For one example of many:
For more about this: International Operations / Traffic Information Broadcast by Aircraft (TIBA).
ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2 2008
ICAO Doc 7030, Amendment 1, International Civil Aviation Organization, 8 January 2009
ICAO Doc 9613 - Performance Based Navigation (PBN) Manual, International Civil Aviation Organization, 2008
Jeppesen Airway Manual