I just finished reading Fredrik Logevall's
Embers of War about this very subject so I have some knowledge of the issue.
You are the supreme commander of all French forces in Indochina and you are battling the illusive Vietminh. Your task is to crush the Vietminh using whatever tactics you have in mind and do it with the best of your abilities. You could also advise/pressure the government in Paris on what needs to be done in order to finish the war and bring the boys home.
Good luck, Commandant. Vive le France
The fundamental issue with the question dovetails with the fundamental nature of the war. The French had the same issue that the Americans would have: conceiving of this war as a conventional war and not an insurgency. Valluy, Le Lattre, Salan, and Navarre all attempted to fight a conventional war in the very same way Westmoreland and Abrams did, and they all failed.
A lot of what needs to be done is in the political realm. The truth of the matter is that France was attempting to defend an unpopular political situation that came about by force following desire for goods, and so their legitimacy in the eyes of the Vietnamese people is very low. This can be improved by public works and attempts to approve the standard of living for the Vietnamese people, especially in the countryside, where the Vietminh did a lot of recruiting. But it cannot be avoided that the French are fighting an uphill battle in this realm.
You as commander must have good relationships in both Paris and Washington. You must keep the goodwill and political fortunes of the likes of Georges Bidault and Joseph Laniel in France and John Foster Dulles and Walter Bedell Smith in the US. Do whatever you can to ensure that Pierre Mendes-France does not become Prime Minister.
You
need American aid, and you need to promote the notion that this is a specifically anti-Communist crusade. This plays well in the US, even if it doesn't in France. Paris may not be willing to provide as many troops as Leclerc would want, but the US can provide support and materiel. Truman, Eisenhower, Kennedy, and Johnson all agreed on this.
depends on how much US is willing to help and pay the bills
Also how much USSR/CHina are helping VC
I would use chemical weapons as much as I can get away with
Using chemical weapons would mean that the war effort loses the vast majority of its support in France as well as a severe curtailing of American aid. The US does not want to be so publicly affiliated with a Western power that uses weapons that not even the Nazis used.
Use soldiers from african countries to offset manpower requirements
Plenty of African troops were used in Indochina by the French. The issue was that there was this fear in Paris that they could absorb the ideology of the Vietminh and then use them to exacerbate the already tense situation there (the Algerian War will break out in 1954 all else being equal), and as such they were not used in high quantities. Using large quantities of African troops leads to the possibility of nationalist uprisings in places far closer to Metropolitan France.
What could
possibly work, and the likelihood isn't great, is to enact a system of internment camps throughout the country to impound every man, woman, and child who could be of use to the Vietminh, not unlike how the British were dealing with the Mau Mau in Kenya at the same time, itself based on British suppression of the Communists in Malaya and going back farther the Boers in the Boer War. This will require a lot of manpower which Paris may not be able to provide, and the system of internment camps will likely lead to appalling human rights abuses as you saw in Kenya (Caroline Elkins has a great book on the subject, and it is
not for the faint of heart). Since this conflict is part of the global war against Communism in the way that Kenya was not, combined with how many fingers the US has in the pie, there is a very strong chance that this will get out to the international media and lead to widespread condemnation and the possibility of the revocation of American aid. It also means that the Vietminh will have a field day in recruiting. That being said, this system
did work in Kenya as it had support in London by the likes of Alan Lennox-Boyd and the Churchill and Eden governments. French politics are substantially more volatile than British politics in this time period so you cannot bank on that sort of support from Paris. If you do enact a policy of internment camps, there will doubtlessly be
buckets of blood on your hands, but it could put an end to the Vietminh as an effective fighting force.
To have the above, you need to either extend the system of camps to Laos and Cambodia, or defend the borders. The former is resource intensive and costly, whereas the latter is almost impossible. China will definitely be supporting the rebels and working against the camps after 1949, which is another wrench in the gears.
The question of success boils down to either improving French legitimacy in Indochina or the capacity to brutally punish Vietnamese society as a whole to take the wind out of the Vietminh. Neither seems particularly possible in the 1950s.