It is notoriously difficult to get an Indian Railway ticket reservation especially during festivals and summer. Now, people use tricks like booking the ticket for a less popular station after your desired destination station( due to a certain quota for each station, they often get it). Tatkal is another option. I want to know more such tricks.
Well this question can never be answered in its entirety because that is the very nature of tricks, you keep discovering them and using them till the time they exist, many tricks that existed in the past have all been either plugged or has been made illegal, however some of the tricks still live on and new ones are being discovered all the time. For the sake of completion and for proper explanation I will include the tricks that you have touched upon too.
QUOTAS (Refer List)
a. Special Category Traveller Quotas
If you are a Senior Citizen (the definition of which is different for Male and Female Passengers) then there is something called Lower Berth Quota which is a set of lower berth seats reserved for Senior citizens travelling alone, when you normally book a ticket this will not be shown and will be visible only at the final booking screen so this qualifies as as trick. There is also a ladies quota in trains and though this is not very common in all trains /classes and station pairs, these quotas can also become handy, physically handicapped, defense, foreign tourist, Yuva are all quotas that you can use to book using these techniques, if there is such a reservation in the said train and you are eligible to claim these quotas as per your circumstances.
b. Station Quotas -
Prior to introduction of computers and network to reserve tickets, Indian railway tickets were booked by alloting a quota for each station and even though this practice has largely been discontinued with almost all stations booking tickets having their own PRS (Passenger Reservation System) terminals, there are still very few of these existing, so if you are using a train which passes through one of these stations, you could go to one of these stations and purchase the reservation ticket offline. I am unable to quote examples as each of these are very local and the area I live in is fairly fully connected to the central PRS network, the Quota codes Road Side, Out Station being still used is proof to the fact that these do exist.
c. Headquarters Quota
In each train, Indian Railways reserve a few seats to be allowed to travel at short notice (this is a very old practice being continued to date even after introduction of Tatkal). The way this works is complex and is completely a discrenationary power of the Commercial Manager at the divisional headquarters of the originating station of you train, there are typically about 3-5% of the berths reserved under this category and you can apply with a specific reason for an emergency travel and the officer may, at his discretion allow you to travel.
Tatkal, Premium Tatkal and Fully Premium Trains
Even though you have mentioned tatkal in your list of known options I am also trying to highlight Premium Tatkal and Fully Premium trains which use an airline-like logic to increase prices for tickets which keep increasing with each additional ticket being booked, in such a case you can always pay more and get a confirmed ticket in most cases
Booking Many tickets
This does not probably qualify as a proper trick as everyone does it but just in case, if you are not sure of the travel date, in an airline you may hold the booking till the last moment, but since Indian Railway cancellation charges are so low, if you are unsure of the dates, book a ticket for the entire week and cancel whatever is not necessary once you have a confirmation of the date.
Change of Names
Indian Railways allows change of names of passengers in some special circumstances so if you are unsure of who in the family may travel or you are a government official and you are not sure which officer may travel, you can book a ticket in one person's name and then transfer it later to the actual person travelling.
Alternate Routes This may not be practical always and is not a trick specific to Indian Railways, but travelling by a completely different route may be a practical thing to search. I will use a picture to explain this. In the picture above if you are looking for a travel from Chennai to Thiruvananthapuram you may not even consider a train going through Tamilnadu (as shown in Option B) as an alternative when booking tickets. The fact that the distance between the Original Destination and the destination in the second option is just 70 kilometers can become useful if you consider this as a valid alternative.
Though these may all sound very difficult to be practical with the traditional tools and websites available, a tool like http://erail.in (I am quoting this website in many of my answers so a disclaimer that I am in no way related to them may be essential) can make these things very very easy. The maps that i have created for the picture used is also from that site. They show quota availability, maps, special trains even information like general delay in specific trains, fare etc.