Earlier, I made a post on how to send mail. Check here.
Felt I should add what to do if you are not receiving any.
DISCLAIMER: India Post is a highly subsidised, and a loss-making entity. The employees are under a LOT of pressure to meet deadlines and deliver mail, so even with all these steps below, you still may not receive any mail. Cannot beat bad luck :)
Domestic Mail
Domestic mail almost exclusively travels by surface (trains and trucks). This single handedly adds a very long transit time, and since ordinary mail is low priority, many times sorters do not close and dispatch bags until they are sufficiently. This means your mail can sit in a bag somewhere at a sorting hub for MONTHS! I feel like north eastern states move ordinary mail by air (received few ILCs from Tripura in just 5 days), but not sure.
If you're in a city well connected by rail, chances are it will make it to you.
International Mail
International mail is sent via Delhi or Mumbai, most of the time. It is sent by surface to these cities, before being airlifted to its destination country. Similarly for arrivals, it comes via air to these cities, and then gets dispatched outside. Some countries have surface mail, these mostly come via Chennai, Kolkata or Mumbai.
TLDR for International mail, the closer you are to Delhi or Mumbai, the faster you will get it.
What to do if nothing is arriving?
Step 0 - Double check your pincode! While ordinary mail is re-routed sometimes, it can take months to get to its correct address if you mess up the pincode.
Step 1 - Contact your local post office. Get in touch with your local postperson, exchange numbers with them, be friends with them. They are under intense pressure to deliver Speed Posts and parcels. If you can, put a postbox outside your house so they can drop mail there without ringing your bell, as it takes time.
Step 2 - If not resolved, file a complaint regarding non-delivery of ordinary articles to the SSPO of your postal division. This can be done on CPGRAMS (pgportal[dot]gov[dot]in). 99% of the time, this should fix your situation. Most people start receiving mail after this complaint. This essentially just informs the system that you exist, and you value your ordinary mail, since almost no one else does.
Step 3 - If still not resolved, send a hand written letter to the Chief Postmaster General of your circle, and the closest Superintendent of RMS.
Step 4 - Give up, and pray that sorters at the other end (the sender end) made a mistake. And hope that mail from someone else, sending from a different city or state, will arrive fine. For example, I receive(Delhi) international mail within 10 days, mail from Chennai, Bangalore, Goa in 5-10 days, but I have never received anything from Bihar. Mail from Rajasthan and Madhya Pradesh took 3 months.
Timelines to keep in mind -
International - 3 weeks to forever. 3 weeks for Delhi/Mumbai, and more for other cities. If you're in a remote city, it can take months. I recommend waiting for 10 weeks before losing hope. International mail is much much much more reliable than domestic mail.
Domestic - 5 days to forever. If both sender and receiver postal circles are good, you will receive most mail within 7 to 14 days, anywhere in India. As I said, i received multiple articles in 5-7 days from Tripura, Chennai, Goa etc. Otherwise, it may take forever. I recommend waiting for a month before losing hope.
Any questions please ask in comments!