The motivations and objectives of the invading group are clear
This one goes without saying., or at least you'd think so. This is a basic modus operandi of story telling. SCUM (in its Steen, Corino, Jacobs form anyway) wanted to make life miserable for on-screen boss Jim Cornette. The Alliance in WWE wanted to usurp Vince McMahon as ruler of the wrestling world. Sadly, some invasion angles, like the UWF invasion of JCP don't even make it that far. SCUM even morphed into something larger, and its motivations actually became a lot more severe (actually making moves to take control of Ring of Honor to kill it), and stayed consistent. However, where the Alliance invasion angle fell through was.....
Individual character motivations have to be clear
Character motivations remain in consistent (except when it advances the story not to)
One of the key issues with the Alliance invasions was that people were jumping ship left and right. Further muddying the water were the multiple titles involved. Beyond its initial expansion in contrast, SCUM and Ring of Honor stayed consistent with who sided with who. The one notable exception is Kevin Steen who left because he didn't like Matt Hardy being boss Steve Corino's top guy. One could argue that this was a weakness in the angle, because it wasn't inferred why Steen didn't like Hardy, Steen just stopped participating in SCUM stuff and looked disinterested when he was there. But I suppose one could also argue that that's subtle storytelling, so it's neither here nor there. Steen's journey provided welcome B-plot to the ROH vs SCUM feud, with the story being "Can we trust Steen?" which was consistent throughout. Compare this to the weeks leading up to Survivor Series 2001 in the WWE, where "Can we trust Steve Austin?" was a problem attributed to the invading bad guys of all people to secure last minute PPV buys. Also, as a side point The invaders must be made to be evil. One of those things that goes without saying you'd think, but even the McMahon spawn only seemed to say some of their best anti-Vince lines for shock value/video packages, and the wrestlers on that team, while heel, still entertained and got babyface reactions. Steve Corino, on the other hand was an irredeemable, evil cult leader who wanted to trample on the livelihoods of the babyfaces for his own petty vengeance, Even though his character wavered somewhat (sometimes he was a Charlie Manson style cult leader, sometimes he was weirdly in love with Matt Hardy, which, as an aside, was my favorite part, sometimes he was very blatantly ripping off Jim Cornette by wearing ugly loud suitjackets and loudly announcing his own men during entrances, and sometimes he was ripping off Heyman on commentary circa 2001). But even for all that, Corino never entertained the fan. He despised the fans and the fans despised him back.
The invaders have to be booked like a threats, with notable wins for the babyfaces
This one is relatively simple, and again, should go without saying. SCUM rarely, if ever, lost, and usually won using criminal methods. If they did lose, it was to advance the story or to provide character development (See: Supercard of Honor VII's main event ) Whereas in the Alliance invasion, or in the UWF invasion, what constitutes threat? Taking one of the 10 available belts and not playing it up like a big deal? Also, I can't recall in the Alliance Invasion Alliance guys ever wanting to cause the babyfaces harm other than to fight them. SCUM kidnapped Veda Scott and severely injured the Briscoes
The final match has to be chaotic and violent (with minimal, sensible swerves)
The 5-on-5 Tag at Survivor Series 200`1 was touted as one of the few good parts of the angle. And while Kurt Angle's babyface turn was a great feel-good moment, the last moment of an angle shouldn't be a swerve.
Now, let's compare that to the Steel Caged Warfare angle that ended ROH vs SCUM. The two true swerves, Matt Hardy getting involved when he wasn't an official participant, and Steen wholeheartedly supporting ROH and winning the match was a feel good moment and didn't leave more questions than answers like Kurt's turn did. However, that isn't to say there weren't additional character moments in Steel Caged Warfare. Jimmy Jacobs preventing Corino from burning Steen alive, and Corino knocking him out, cemented Jimmy as a babyface post angle, and didn't take away from the end of the angle itself.