How to make a sequel besides having a lot of investment cash and random ideas? Well, the random ideas part has got me in the ballpark. By the way, this isn’t the way to necessarily make a good sequel. This may be to just keep the series trucking along to hopefully the point that the future movies that might possibly be better. Quit laughing it could happen if the title doesn’t include the words "PupperMaster".
1. Nothing tends to fire up a sequel which in this case is probably bad faster than including the word "Final" in the title. Friday the Thirteenth didn’t quite start generating sequels quite as fast as until after hitting the Final Chapter.
2. Make it a crossover between monsters. The monster battle royale doesn’t need very much plot development. After all, how many shark and croc/gator battles have been made in the past few years? There have been plenty of others: Dracula versus Frankenstein, Freddy versus Jason, Godzilla versus everyone else, or the vampire/werewolf fights to romantic epics in the currently very lame bad fanfic style.
3. If you can’t sequelize it, your duty is to prequelize it with at least one character that is to the point of fingernails raking across chalkboard(Jar Jar Binks). Ask George Lucas about that.
4. It may be a better idea to not overload one movie by spreading some major plot points over several movies. Ask Peter Jackson about this.