Tip #1: NEVER pull a sickie on a Monday or a Friday, much too obvious.
#2: Plan ahead. The day before your sickie start feeling quite unwell while at work. Everything's a struggle, an effort, a bit of moaning and groaning for effect, lots of sit-downs and water breaks, but "soldier on" thru it and see the day out. Under no circumstances allow yourself to be sent home,
#3: Easy-peasy. Phone in sick the next day. Whatever illness you've decided on followed by "I've been up most of the night/had a terrible night" etc, "I'm going back to bed now to see if I can sleep it off. I'll definitely be back in tomorrow" blah blah.
#4: Don't go back in tomorrow. Phone again, not quite as early as the day before. "really sorry. Thought I'd be over it by now" and so on. BUT THEN turn up at lunchtime. Continue the performance from the set-up day. "I really couldn't justify a second day off/ If I'm well enough to be out of bed I'm well enough to be at work"etc.
Follow these hints and no-one will doubt you, and in the future you'll have no-questions-asked sickies, because you came back to work as soon as you could, still ill and so on.
Good luck!!