Get to court nice and early - if the other side are represented, this will be an opportunity to agree on anything capable of agreement and exchange legal authorities.
As the Claimant, you should "open" the case - ie tell him what the case is about, how you put your case and how the Defendant puts his. However, many Judges with a litigant in person will dispense with this.
After the opening, you give your evidence (which will be based on the witness statement you should have done). you will then be cross examined by the other side. You then call your other witnesses who will also be cross examined.
After you have called all your evidence, the roles reverse and the Defendant calls his. Once he has given evidence you should cross examine. This is difficult to do if you have never done it before. You need to test his evidence by questions, eg
Do you accept that on 15 March you ordered 10 widgets from my company?
And those widgets were delivered on 16 March?
They were in good condition?
You say not, in which case, why didn't you raise this at the time?
You should also "put" your case to the Def.
After all the evidence, the Defendant makes a closing speech, followed by you. You cannot introduce new evidence here but should use this to persuade the Judge that your evidence is to be preferred and explain the legal basis for your claim and what authorities support it.
As the Claimant, you have the burden of proving the case on the balance of probabilities.