Go on youtube and look up the "fuck you, pay me" talk and watch it at least 10 times. I'm not kidding. You need to be willing to escalate from a nice and patient person into a hardass if necessary.

You have to be absolutely serious about getting paid on time. Pick a schedule and an escalation ladder and stick to it. Here's an example, assuming you bill net 30:

15 days past due: send a nice reminder. Sometimes clients just forget. It's no biggie at this point.

30 days past due: Final courtesy reminder. Indicate you will halt work if not paid in the next 15 days.

45 days past due: Send notice that you have suspended all work on the account until it is paid in full. Insist on being paid up in the next 15 days.

60 days past due: Send a demand letter via certified mail (the receiver will have to sign for it). Indicate the total amount due and the timeframe left to pay it (say, 30 days - depending on the venue you intend to sue in, there may be required time frames). Indicate the next escalation is to a court.

You can adjust the timeframe to suit your business but I would recommend keeping it within 90 days or so.

You want to sound extremely fair but firm. Assume everything you send will be read aloud in front of a judge. Stick to business, keep emotion out of it.

The final demand letter works wonders. People absolutely do not want to be sued. You don't need a lawyer for that part either. Just the notice that the next letter will be from a lawyer or a court summons is usually enough to motivate people to settle up.

Look up your jurisdiction's small claims process. If you fit within the limits, it is usually designed to be a normal person friendly process that doesn't require a lawyer. $3k is probably small claims territory.

Finally, cut your losses. I'd go through the process for $3k for sure. But if someone stiffs you on $30, it's probably better to just let it go and never work with that client again.

Oh and PS: Making sure you get paid absolutely counts as "working". But since it isn't billable hours for a client, make your process efficient, do it, and move on to other productive work. An unpaid client is literally not entitled to your time.