Serve if you want your group to be loose and in the mood for dancing.
A bit loose (like you, after you have drunk several?) No, seriously, the ingredients change a bit, depending on what fruit and what juices I have in the cupboard, but I will tell you what we used on Saturday.
Vary quantity depending on how humorous you want the group to get. I used mainly gin and just topped it up with rum, but that was because the rum was dark rum. I would mainly use equal measures of white rum and gin.
A nice variation is white rum mixed with a coconut cocktail (like Coco Ribe), which is itself white Rum mixed with Coconut Water. I dribble in some Coconut cream for added flavour.
Depending on the quantity of drink you are making, add more bananas. For a blender full, I usually use 2 bananas. Make sure they are nice and ripe (with freckles on them).
Pawpaws and pineapples are also an absolutely great fruit to use in these, and nice when you also use all three together (with the bananas I mean).