It is my contention that Christianity in the West has been all-but defeated by Leftism - and that Leftism is itself a thing which has evolved as an anti-Christian ideology.
This means that modern Leftism has evolved in what was originally a Christian context to damage, subvert, destroy and invert Christianity. Because Leftism evolved in a Christian context, Leftism is pre-adapted to thwart most of the historical strategies of Christianity.
In other words, when considering strategies to promote the future of Christianity, if a strategy has been tried and failed in the past, if a type of Christianity has been defeated by Leftism; then it is unlikely to work in the future.
(So long as the Leftist West stands. If any type of Christianity survives until after the West collapses, then it may well be in a position to exploit and thrive in the very different post-collapse situation.)
In other words, an attempt at straightforward revival of some past type of Christianity which is currently failing is not likely to work as a strategy for Christian revival in the current context.
How can we evaluate success or failure?
Biologically, any potentially successful and robust religious group needs to have a viable demographic structure: above replacement fertility, an age profile less than forty, a sex profile with about half men (or higher).
If a type of Christianity clearly lacks these (i.e. if it has significantly below replacement fertility, and age structure dominated by the elderly, and is composed mostly of women), I suggest that this is a sign that it has been defeated by Leftism, Leftism has the better of it; and we cannot hope realistically for a Christian revival from such denominations or churches.
Spiritually, since we cannot look into Men's souls we are forced to rely upon objective indicators. So, the viable type of Christianity will demonstrate evidence of devoutness - adherence to a demanding lifestyle, high levels of tithing, church service, missionary activity, strength in the face of persecution etc.
Such criteria could serve as a basis, as a beginning at least, for understanding of what might work (best to pursue several lines of strategy), and perhaps what ought to be done - to trigger and build a Christian revival.
Note: I also think that success is more likely from scaling-up a small but successful group, than from trying to reform a large group that is mostly a failure but contains minority pockets of success. At least, this is what happens with other human institutions. When the successful parts of an organization are in a small minority, it can be very difficult or impossible to reform the organization - unless there are first massive, majority 'cuts' to get rid of the negative, destructive influence of the failing majority. On the other hand, small successful institutions and businesses can often be up-scaled ten, a hundredfold within a very short timescale.