By statist standards, the Weinberger Doctrine is a sound, deeply reasoned and frankly pragmatic doctrine that gets plenty of lip service but no real world observance in the 21st century in American foreign policy and export of violence. One would be hard pressed to come up with a guiding template that more keenly fuses Clausewitzian realism with Tzu’s admonitions for the “indirect approach.”
(1) First, the United States should not commit forces to combat overseas unless the particular engagement or occasion is deemed vital to our national interest or that of our allies. That emphatically does not mean that we should declare beforehand, as we did with Korea in 1950, that a particular area is outside our strategic perimeter. 
One can observe that this was certainly the case with Afghanistan in 2001 even though the deployment of conventional forces prematurely after the burgeoning success of the Northern Alliance to best the Taliban with US/Allied special operations assistance spoiled the recipe in place for a long-term self-determination.
The US had no such national interest in hand despite the 21 causus belli enunciated by President Bush during the run-up and actual invasion of Iraq. Tremendous intelligence tension was evident and Defense Secretary Rumsfeld was so affronted by this that he stove-piped and forced conclusions with his Office of Special Plans to convince the skeptics that a removal of Saddam Hussein was necessary. The concomitant disastrous missteps of the dismantling of the Iraqi military and the evident ignorance of the resistance brewing to American long-term intervention went unheeded and history tells the rest of the story.
(2) Second, if we decide it is necessary to put combat troops into a given situation, we should do so wholeheartedly, and with the clear intention of winning. If we are unwilling to commit the forces or resources necessary to achieve our objectives, we should not commit them at all. Of course, if the particular situation requires only limited force to win our objectives, then we should not hesitate to commit forces sized accordingly. When Hitler broke treaties and remilitarized the Rhineland, small combat forces then could perhaps have prevented the holocaust of World War II. 
GEN Shinseki lost his job as America’s top Army General because he refused to submit to rosy predictions and ludicrous force projections necessary to sustain a long-term occupation of what was becoming the birth of several Islamic republics in the vacuum left behind by Hussein’s brutal yet essentially secular Arab state. The US simply did not have the force structure or culture to occupy and transition the country to a state that would be neutral or beneficial to American national security interests in the region. Optimistic talk of increased oil outflow to Western countries and the discovery of mysterious weapons of mass destruction (outside of US supplied chemical weapons) saw no fruition.
(3) Third, if we do decide to commit forces to combat overseas, we should have clearly defined political and military objectives. And we should know precisely how our forces can accomplish those clearly defined objectives. And we should have and send the forces needed to do just that. As Clausewitz wrote, “no one starts a war — or rather, no one in his senses ought to do so — without first being clear in his mind what he intends to achieve by that war, and how he intends to conduct it.” 
The objectives kept changing over time for the entire theater. In Afghanistan, it was at first the removal of the Taliban then it became the creation of a Western state that would increase women’s rights and suffrage in an Islamic nation in cooperation with Pakistan which had actively supported and harbored the Taliban and Al Qaeda during the entire prosecution of the war. In Iraq, one could find no milestone of strategic or grand strategic value and in a counterinsurgency (COIN) conflict, this is a slow death for occupation forces who are asked to work in a haphazard and whimsical fashion as the policy vacuum slowly grows larger and more mercurial over time.