Most roleplayers have little to no practical experience in military strategy and tactics. So when it comes to playing massed combat situations, one way to decide what to do is to take guidance from historical military campaigns.

Emulating the victor is the easy way. If attempting to defend an impossible position with bowmen and knights on foot against Genoese crossbowmen and tens of thousands of armoured, mounted knights, make sure you are heavily outnumbered. If attempting to repel a force of cavalry and men-at-arms with longbowmen on St Crispin's Day, make sure you are vastly outnumbered. If defending a hospital stockade against Zulus, make sure you are enormously outnumbered.

You can choose a different, and more creative, path by doing the opposite of what the losers did. If you field an overwhelming force against a paltry number of defenders, whatever you do, make sure the defenders are not English!

Transcript

Yoda: Pe-ete! Why are you ordering a charge?!
R2-D2: Two words: New dice!
R2-D2: Look, they're precision carved from six different types of wood, including black ironwood and Lignum vitae, the hardest and densest woods known.
Yoda: Somebody's being dense! The Wookiees will get slaughtered!
R2-D2: No, by charging we get a surprise bonus on initiative. The clones can lay down suppressing fire. And if we hit the droids in the water they get -2 to Dodge.
R2-D2: Besides, these stupid combat droids have never won a battle in the history of ever.
Yoda: But why do we have to charge, when we have ranged weapons?
R2-D2: This is just like D-Day. And the Wookiees are the Germans.
Yoda: What?
Obi-Wan: The Germans didn't charge the Allies.
R2-D2: And they lost!!