Group tickets by company
Link every contact to a company record, usually by email domain. Anyone on the team should be able to see all open and recent tickets for that company in one place.
Name an account owner
Assign each larger customer to one agent or lead who knows their setup. Others can still reply, but the owner sees the pattern and handles the sensitive conversations.
Keep short account notes
Write down what is unusual: a custom integration, a billing arrangement, a contact who prefers calls. Put it where every agent sees it when they open a ticket from that company.
Treat the admin differently from users
The person who pays or manages the account has different needs from a daily user. Mark who they are, and tell them when a problem affecting their team is fixed.
Escalate on account risk, not only on severity
A small bug from a large customer who is renewing soon may deserve faster attention than a bigger bug from a trial. Agree who decides, and write the rule down.
Review accounts regularly
Once a month, list the companies with the most tickets or a rising trend. These accounts need onboarding help, a call, or a fix to something in your product.