How do you get a software patent?

Not so much special requirement but there are certain traits that it needs to pass the bar against pure functional claiming (loosely speaking this is where trying to patent the problem and not solution). The recent US Supreme Court ruling on Alice moved the bar higher towards requiring an inventive concept sufficiently transformative, not just instructing the practitioner/computer how to implement the steps. The problem with finance is that if you are solving an existing issue, then better, faster cheaper doesn't really cut it for software. It needs to either use completely new approach (eg cryptocurrency) or has properties (stability, security, etc) that cannot be available using existing methodologies ... BTW, your concept of strong IP is slightly skewed, copyright is strong in the sense it protects cloning by competitors but patents are NEGATIVE rights, the ability to exclude others from the precise implementation but that just means peers look for work-arounds (see the recent Akamai ruling). On the other hand, customer relations (trade secrets) reputation (brand) and network effects are also strong in their own way. It all comes down to a matter of risk but trying to control new entrants is like defending against a botnet, too many directions a threat can come from so if the patent is not distinguishable and defensible, then it is just nice wallpaper

By filing a patent application with a well-drafted specification and prosecuting same to grant!
Naturally, the details depend on the requirements of the national or regional patent office examining the patent application.
If you may consider to file - later on - a patent application in Europe, for example a European patent application to be examined at the European Patent Office (EPO), the specification should already be drafted under due consideration of applicable requirements!
In Europe, patents are generally granted for any inventions in all fileds of Technology, provided that they are novel, involve an inventive step, are suspectable of industrial application und are regarded as inventions. Among other things, business methods and Software AS SUCH are not regarded as inventions.
So, in principle, computer-implemented inventions (CII), i. e. inventions implemented in software, hardware or a combination thereof, are patentable inventions.
Having said that, the main reasons for refusing CII patent applications - after examination of the TECHNICAL features - are lack of novelty or lack of inventive step.