If you insist on negotiating yourself, here's a primer to get you started:
DO have a story explaining specifically why you are having trouble paying the debt. Maybe you had a period of unemployment; maybe you went through a divorce or had a significant illness. These are all reasons to get a lower settlement amount.
Do NOT call the company and immediately offer a settlement amount. You have no idea what they are going to offer you. It could be much less than you are willing to pay. Let them make the first offer.
Do NOT call the company
unless you have the money. Sometimes they will accept a payment
plan, but that will cost you more. A lump-sum payment will always
be your cheapest option.
Do NOT give the agency any more information than your name and
account number. Don't tell them where you work; don't tell them
your current address. They can ask ... and you can ignore them
and go back to negotiating. If they press you, simply say, "I
don't want to waste your time. Please don't waste mine."
Do NOT let them report this account as settled on your credit
report. A settled collection account is as harmful to your credit
score as a delinquent account. Offer your payment in full (and
be willing to pay a little more) if they will remove the negative
mark. Many collection agencies will do this because they want
to be paid. If you cannot get the account removed, then try to
get them to report the account "paid as agreed."
Do NOT act timid. Believe it or not, you are in the power position,
because most people do not proactively contact collection agencies
to pay their debt. You are making their job easier. That gives
you the right to demand a better deal.