In bad sci-fi movies, we show the monster right away, right after the opening credits. That eliminates that nasty ol’ tension and sets you free to admire the special effects at leisure.
As someone who has seen BloodMonkey and Rock Monster (twice - ooh, and that cliffhanger ending left room for a sequel!), I can confirm how important this is.
Firstly film everything with a small dead fly on the camera lens.
Mistime the lip sinc by juuuust a fraction.
Have the hero as an American but played by a non American actor with an appalling American accent.
Likewise have an Irish sidekick played by an American actor with a dreadful "Hollywood"Irish accent.
Include an English character who speaks in an upper class accent but uses Cockney stereotype expressions, as in “Cor Blimey Guvner,strike a light why dont you me old cock sparrow”
Misuse astronomical terms frequently,"He comes from the Xanadu galaxy near the planet Zorg in the constellation of Aries the Ram.
And the plucky kid (who has no real reason to be the pipe-using scientists best buddy) says “Golly! That’s 67 million miles away. I bet it takes him over 20 light years just to get here!”
The Comic Relief (or, the Comic Sore Thumb) - The dense character that provides the perspective of the audience in a groan-inducing manner, and always voices just how bizarre the situation is that they happen to be in. Bonus points if they make reference to a popular sci-fi franchise, and how it relates to their situation.
Include shots of instantly-recognizable landmarks in non-American cities (Big Ben, the Eiffel Tower, the Pyramids at Giza, the Taj Mahal) shortly before those cities are destroyed. Include no non-American characters, or at least restrict them to minor roles strictly reactive to the Americans, with no original thoughts or actions of their own.
Shots of the main characters with inappropriate facial expressions and/or vocal expressions, intercut with the shots they’re allegedly reacting to. Making it clear that they’ve been coached to react to something other than we’re being shown in the final cut.
A very short stock shot of screaming people running, including an attractive topless woman. For no reason other than to solidify the R rating and attract hopeless geeks with the prospect of nudity.
Regardless of where the movie begins, the finale of the film must be set in New York City. The monster/aliens/big bad wolf MUST rampage through NYC, and specifically Manhattan, not the outer boroughs. No exceptions, no substitutions. It must be in Manhattan. There must be at least one shot each of the Empire State building and the Statue of Liberty. The Brooklyn Bridge must be ripped apart. (Not the George Washington, Tri-borough or even the Manhattan bridge. It must be the Brooklyn Bridge.)
There must be a villain with a distinctly upper-crust British accent.
Keanu Reeves must star in it.
Early on in the film, some secondary character must scoff at the idea of aliens, killer monsters on the loose. He must utter dialogue along the lines of “What do you think this is? Some kind of B-grade sci-fi movie?” Then get promptly eaten.