Your question suggests you did not access Leo Paquette's Encyclopedia of Organic Reagents (14 volumes, some schools have access to the electronic version eEROS), or its one-volume siblings by topic, e.g., Oxidizing and Reducing Agents (this one by Burke and Dannheiser). These resources cover physical / chemical properties of frequently used reagents and briefly showcases a selection of typical applications.
Citing the entry about $\ce{MnO2}$ of the former source, one of the of early hints preceding the protocols to prepare $\ce{MnO2}$ states for example
«It is worthy of note that the percentage water content strongly influences both the oxidizing power and the selectivity (oxidation
of multifunctional molecules) of active $\ce{MnO2}$. Thus it is well
known that the wet material (40–60% $\ce{H2O}$) obtained after filtration must be activated by drying (heating to $\pu{100–130 ^\circ{}C}$ for
$\pu{12–24 h}$ or, better, at $\pu{125 ^\circ{}C}$ for $\pu{52 h}$). Indeed, an excess of water decreases the oxidation power since, according to
the triphasic mechanism generally postulated, it would prevent
the adsorption of the substrate to the oxidatively active polar
site on the surface of $\ce{MnO2}$.»
The first of the six protocols presented is the basic one by Attenburrow (beside protocols under acidic conditions, by pyrolysis, coating silica gel with active / activated $\ce{MnO2}$, etc.) and reads as
«A solution of $\ce{MnSO4 ⋅ 4 H2O}$ ($\pu{110 g}$) in $\ce{H2O}$ ($\pu{1.5 L}$) and a solution of $\ce{NaOH}$ (40%; $\pu{1.17 L}$) were added simultaneously during $\pu{1 h}$ to a hot stirred solution of $\ce{KMnO4}$ ($\pu{960 g}$) in $\ce{H2O}$ ($\pu{6 L}$). $\ce{MnO2}$ precipitated soon after as a fine brown solid. Stirring was continued for an additional hour
and the solid was then collected with a centrifuge and washed with water until the washings were colorless. The solid was dried in an oven at $\pu{100–120 ^\circ{}C}$ and ground to a fine powder ($\pu{960 g}$) before use.»
Probe which of the protocols works well enough for the application in question. Since eEROS points to the primary literature which you may combine in a subsequent search in Reaxys, Science of Synthesis, SciFinder etc., you equally may see which of them are applied on substrates similar to yours.
References
Cahiez G.; Alami, M.; Taylor R. J. K.; Reid, M.; Foot, J. S.; Fader L.; Sikervar V.; Pabba, J. Manganese Dioxide in Encyclopedia of Reagents for Organic Synthesis; doi 10.1002/047084289X.rm021.pub4.
Attenburrow, J.; Cameron, A. F. B.; Chapman, J. H.; Evans, R. M.;
Hems, B. A.; Jansen, A. B. A.; Walker, T.. 194. A synthesis of vitamin A from cyclohexanone. J. Chem. Soc. 1952, 1094-1111; doi 10.1039/JR9520001094.
