In Act I, Scene 2, Casca tells Brutus and Cassius that Antony wanted to give Ceaser a crown after the race. Ceaser did not take the crown and the citizens "hooted, and clapped their chopt hands" (I:ii: ln 244) for Ceaser. This is important because it shows that the citizens like Ceaser because he didn't take the crown. What they don't know is Ceaser is just tricking them into believing that he doesn't want the crown but in reality he really does want it.
Act IV: Sc
In Act II, Scene i, the conspirators talk about killing Ceaser. Cassius talks to Brutus about joining the conspirators and killing Ceaser. Cassius wants to kill Antony too but Brutus says that killing him is not necessary. Later on in the play they find out that they probably should've killed him.
Act V: Sc
In Act III, Scene 1, the conspirators go to the capital with Ceaser to kill him for the good of Rome. Ceaser had warnings that something was going to happen on then Ides of March. Artemidorus says "O Ceaser, read mine first; for mine's a suit That touches Ceaser nearer." (III:i: ln 6-7) and then Ceaser says "What touches us ourself shall be last served.". (III:i: ln 8) Ceaser just ignores these warnings and in result gets killed.
In Act IV, Scene iii, Brutus and Cassius set up a fight with Antony and his men. Cassius wants them to come all the way to them. Brutus says they should meet them in the middle so they surprise them. If they came all the way to them then they would've gotten reinforcements.
In Act V, Scene iii, they all fight in a huge war. Brutus wins his battle against Octavius. Cassius loses his battle against Antony because Brutus said they were ready and he wasn't. The messenger said that people got captured by the enemy so Cassius kills him self. They were actually Brutus's men celebrating the victory.
The theme of this story is to take care of things before they even become a problem. They showed this by killing Ceaser. They should've just killed Antony too but they didn't because Brutus is too nice. If they would've followed the theme they wouldn't of had a war and all those people wouldn't have died.