Cassandra is one of those characters who can play just about any style of offense, but is not great at any particular game plan. Her collection of moves allows Cassandra to apply an aggressive short pressure game, an evasive 8-way run marathon, or a passive poking game.
On defense, Cassandra's wide range of tools also gives her the option to make it difficult for any opponent to contain her, whether it be trying to space her out at a distance or a short pressure barrage.
The best advice for using this versatile character is to not fall into repetition. Cassandra is one of those characters that either thrives or dies depending on the combination of her opponent and the offensive game you wish to use. Learning to adapt is key for success with any character, but it is especially important for characters like Cassandra who are not particularly overpowering or lacking in any one category.
Beginner Cassandra players should consider experimenting with Slide Flow, Slide Rush (A, B, B), Slide Sweep (A, B, K) and Slide Tornado (A, K) as good starting points for either a poke or strong offensive game. Almost all of these are good solid offensive strings that offer some minimal variety with easy execution (Slide Sweep in particular offers a nice High Low mix up).
Some good Cassandra players swear by the mind games you can play with Angel's Exile and a combination of her other quick QCF/QCB moves (too many possible variations to list here, so check out her full move list). The move is quick at putting Cassandra in and out of medium to short range and is great for pressuring opponents into a ring out situation. Just don't become too predictable by sticking to only this one move. Experimentation with this Angel's Exile, and its variations, is a must.
This is pretty much the same idea as the A examples of simple offense. This move in particular can upset the orientation of the match if landed as well as lead into a number of other moves or situations for Cassandra. Also check out some of her simpler B moves like Dancing Shield (B, B), Shield Nova (B, 6, B) or Angel's Rush (6, 6, B, B).
Click here to see all of Cassandra's moves