This is a brief, step-by-step guide for getting into plexing guristas, in response to a comment on a previous post. Other types of plex (angel, serpentis, etc.) would typically mean doing the exact same thing but with a different tank ship and damage types. For ishtar fittings and comments please reference my earlier Ishtar-vs-Guristas post.
There are five things you need to do in order to plex.
First, find the plex and get your plexing ship to it. The first part isn't really very hard -- you just need scanning skills. Although a covert ops ship with gravity capacitor upgrades would be best, you might note the solo plexing ishtar fit from my ishtar-vs-guristas post linked above, which even though it lacks any sort of scan strength bonus is apparently able to find the tougher solo plexes (e.g. pith's penal complex) with good skills.
The ishtar is a pricy piece of hardware though, and I wouldn't fancy slowboating it around a region without good intel. If you have two accounts it would be good to use a cov ops scanner as a scout, or better yet a scanner/scout that adds damage such as a T3 with covert reconfiguration and scan bonus, or a covert ops to scan then switch to a stealth bomber with torpedoes to scout and do damage.
Second, know the plex. This part is easy -- the eve wiki lists most plex and is mostly accurate. The ones that have a 180,000 damage EM torpedo in the last stage? Stay away from those until you have a plan for surviving it.
Third, you need to tank. If you don't mind burning through cap booster 800s and have somebody to do actual damage, you can do this in a scorpion with an x-large shield booster. Less horrible options include a passive-tanked nighthawk (if you don't mind doing no damage), possibly a passive-tanked gila (very similar to ishtar, but less damage and tank) or, best of all, an ishtar.
Finally, you need to do damage. Once again the ishtar wins, dealing over 500 DPS with good skills. If you'd like to step things up though, a third account can be fit for pure DPS (since the tank has aggro) -- and at that point you can easily pay for all your accounts with isk.