By going with the "Norway Option." Like Norway, Pakistan faces a militarily superior military with a budget several times greater in magnitude. Yours is India, ours is Russia.
Options for credible deterrence:
1. Partner with a larger force. We have NATO, the EU Battlegroup and most importantly, the US. While China's commitment to Pakistan's defense is untested in real terms, China does provide Pakistan with enough leverage to keep India off-balance via the "two front war" scenario. India can't concentrate on Pakistan alone and must divert funding and resources to maintain its military presence on its border with China and in seas/oceans now being frequented by Chinese warships.
2. Make war hurt. Taiwan is a classic example of a smaller, less sophisticated, less capable military acting as a deterrence to a larger force. Interceptor aircraft keep its skys clear, coastal artillery and missiles its sea-lanes contested and a small, but notable submarine force China's navy busy.
Similarly, Pakistan can employ the same strategy, but with "Pakistani characteristics." Under this scenario, Pakistan would leverage naval strike options - such as the JF-17 and C-400 to keep India's navy at stand-off distances, it would use its submarine force, currently being upgraded via a deal with China, to further back the IN away from Pakistani shores and shipping and its land-based missile force should be sufficient enough to strike against large, fixed targets such as political centers and military bases. Currently Pakistan needs work on ensuring its missile can negate or break-though Indian air defenses, and its naval air and sea assets will come under an increasingly large capable counter-force, but the principle remains, it's the scale that Pakistan needs to improve.
China employs such in the form it A2/AD:
3. Non-traditional warfare has been a staple of Indo-Pakistani relations since the two nations split, this relationship keeps them both off-balance, diverts resources and keeps the other nation honest. Pakistan, whether it admits to it or not, can fund militant groups in India that can be used to harass, demoralize and undermine India military effectiveness by sabotaging infrastructure, conduct psychological operations against Indian personal - such as gas lighting, and by conducting direct actions against important Indian targets.
The concern here is a return-of-the-favor.
4. Take advantage of India's often times poor procurement policies and bureaucracy that ham-strings its military development. India is underdeveloped militarily, and it's situation, while improving, still isn't anywhere near good enough, as noted in its Rafale and artillery tenders. If Pakistan can streamline its own procurement and iron-out its procurement necessities, it can better adapt to India before India even knows what it wants.
A classic example:
5. Leverage India's regional concerns. This goes along with point one, but Pakistan needs partners, not adversaries. If Pakistan can better its relations with Bangladesh, Myanmar and other regional nations, they can pin India into a corner and keep it honest in its military dealings. Encirclement overstretched already overstretched militaries, the Soviets found this out the hard way and spent unnecessarily to keep up with ever growing threats. If India's threat profile increases in its regional neighbors, it too will have to react to negate or mitigate that threat.
6. While military options are important, they are also expensive. Pakistan must continue with economic reform and progress. While some of the above options are fiscally doable on a smaller budget, such as funding proxies and militany groups - it's politically costly and the potential for these groups to turn on their host is a constant concern too, most of the options Pakistan can or will exercise require money... a lot of it.
Subs, frigates/destroyers, aircraft, missiles, these aren't cheap. Focus on the economy more-so then the military, but without completely neglecting the military either. Maintain a minimum credible deterrence and once the economic situation improves, shift military expenditure into high gear.
A great economic initiative:
7. Once the economic situation improves, its time to ask yourselves, "what's next?" What's the next phase, the next plane of battle that we are likely to encounter? What system can give us an edge? Perhaps Pakistan can invest more in space? Develop your launch and satellite capabilities. Developing launch methods also helps domestic ballistic missile programs, often SLVs are derived from ICBMs or ICBMs are derived from SLVs. The development of long-range rockets, which can become missiles with the inclusion of a guidance system, can keep far-off powers honest too via MAD.
This also opens up the possibility for spy satellites, communications nodes and ASAT options which improve Pakistan's flexibility, allow it redundancies which make it less brittle and increase the headaches that India must account for and spend to counter.
US "Inspection Satellite" MiteX A
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There you go. My thoughts on how Pakistan maintains a credible deterrence against a larger power
I'm not sure how much of a deterrent you'd be though.
