Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Breathing or swallowing difficulty, swelling near the eye, or rapidly spreading neck or facial swelling requires emergency care.
Seek same-day dental or medical care for new fever, increasing facial swelling, worsening pain, or reduced ability to open the mouth.
Follow-up depends on the treatment performed.
After drainage, root canal treatment, or extraction, some soreness and local swelling can occur.
The dental team should explain what recovery is expected and when the tooth needs to be rechecked or restored.
Routine prevention focuses on reducing decay and gum disease.
Brush with fluoride toothpaste, clean between the teeth, limit frequent sugary snacks and drinks, and attend dental visits at intervals recommended for your oral health needs.
A dentist can also assess dry mouth, worn fillings, cracked teeth, and other problems before they lead to a new infection.
Routine follow-up is appropriate when symptoms are improving and there are no signs of spreading infection.
The article also says
Contact the treating dentist if pain or swelling is worsening rather than improving, drainage continues, a temporary filling comes out, or prescribed medicine causes troublesome effects.
If antibiotics were prescribed, report symptoms that fail to improve as expected.
A root-canal-treated tooth may need a permanent filling or crown.
Delaying the final restoration can leave the tooth vulnerable to leakage or fracture.
Periodontal abscesses may require ongoing gum care and more frequent cleaning.
Every sign above is quoted from the sofidex article on Abscessed tooth. If you are not sure, err upward — it is always reasonable to be checked.