We have exactly one story of how this process occurred in the universe (so far)- our own.
Our story in short is of a derived social primate with binocular vision, a workable set of hands transitioning by phases from foraging to scavenging to predation using tools at every stage rather than developing any biological kit other than a brain and body suitable for diurnal endurance hunting.
Viewed in reverse, its a plausibly straightforward process. In other words, not that hard to conceive of it occurring by stages. At every next stage, niches were available - bones full of marrow laying around unclaimed, predators sleeping in the heat of the day with prey abundant, the ability to forage in compensation for any shortfalls on the meat line of pursuit, varying climactic conditions driving a brutal winnowing for adaptability on the main organ of selection, also the social/sexual selection.
Can you envision a process whereby a cetacean or cephalopod or ungulate or carnivore or arthropod or some other order/clade - or alien analogs/alternatives- could, in any comparably straightforward process, or even less straightforward process for that matter, find its own gradient to evolve a comparable socially-based intelligence?
In simpler English: Can you plausibly imagine such an alternative to a peer species arising, and if so, how might that be?
- The aliens, or next wave of sentient animal to arise on this planet, could have arisen from scratch on a young planet, or post planetary extermination event (e.g. nearby supernova) or from a pruning of existing life such as occurred via the k/t mass extinction event. Sentience, in any case, comes late in any life process, at least in our singular example. The late stage is the key, not the long process before.
I have a strong bias, and it is a bias, toward what I've seen work, have some notion that I understand roughly how it works, and thus tend to view phenomena, where unique, as having certain likely intrinsic requirements - such as water/carbon based life being astronomically more probable than any conceivable alternative, as one example. But that may just be a failure of my own imagination. Others, in my opinion, ignore constraints, or aren't aware of them, and let their imaginations run wild :)