Preparing a newly dead patient for the long-term low-temperature storage offered by cryonics is a medical procedure - and as such just as potentially complicated as any other aspect of human medicine. A great deal of time and effort over past decades of the cryonics community has gone into developing the best-practice procedures presently used, but often overlooked by those who discuss cryonics.
A dense, informative post over at Depressed Metabolism examines this in some detail, including the present gaps in knowledge, resource constraints, and areas where improvement is desirable:
Is a patient who has suffered hours of warm ischemia better off simply being rapidly cooled and rendered into the solid state, as opposed to being subjected to 24, 48 or 72 hours of cold ischemia, followed by cryoprotective perfusion and freezing or vitrification? How do we even determine what the ultrastructural condition of a brain is following straight freezing? Freezing in the absence of fairly large amounts of colligative cryoprotectant agent(s) results in the collapse of tissue ultrastructure into dense channels of material, the structural condition of which it is currently not possible to determine by techniques such as transmission electron microscopy. Reaching conclusions based on the post-thaw ultrastructure (or lack thereof) of straight frozen tissue is complicated by the potentially myriad artifacts introduced during rewarming, thawing, fixation and embedding required to image tissue ultrastructure.
Given the extreme resource constraints that have historically been present in cryonics, and the lack of directly applicable mainstream medical research, the answer to the question of 'what to do' has been to apply reasoned extrapolation of high quality, peer-reviewed biomedical research to the care of the individual cryonics patient, and where possible, to conduct on-point in-house research to validate such armchair speculation.
Preserving the fine structure of the brain is vital to the endeavor of cryonics. While evidence exists that even simple freezing at liquid nitrogen temperatures might preserve enough for future revival through applied molecular nanotechnology, many open questions remain as to how important the quality of preservation is, and what methods of preservation best preserve the information stored in the brain. All other matters being equal, we'd expect a carefully vitrified brain to be easier to restore than a frozen brain, and we'd expect a brain preserved more rapidly after death to be easier to restore than one left for longer. But hard and fast evidence to back that up is somewhat lacking.
However you choose to educate yourself about cryonics, it should be clear that even if flawed, cryopreservation is the best post-death choice - if you like living, that is. Nothing else will yet give you a shot at being restored to live more productive, healthy years further down the line, and nothing else presently envisaged will do anything to help the hundreds of millions who will most likely die before the advent of effective rejuvenation medicine.