Summarize:

Ask them to do something specific:

Don't say, "Help the Red Cross"

That's too general.

Say, instead, "Send your enrollment fee of one dollar tonight to the American Red Cross, 125 Smith Street in this city"

Ask the audience for one response that is within their power to give.

Don't say, "Let us cast our ballot against the Demon Rum"

It can't be done. At the moment, we aren't balloting on the Demon Rum. You could, instead, ask them to join a temperance society or to contribute to some organization which is fighting for prohibition.

Make it as easy as you can for your audience to act on your approval.

Don't say, "Write your congressman to vote against this bill." Ninety-nine per cent of your listeners won't do it. They are not vitally interested; or it is too much trouble; or they will forget. So make it easy and pleasant to act. How? By writing a letter yourself to your congressman, saying, "We, the undersigned, urge you to vote against Bill No. 74321." Pass the letter around with a fountain pen, and you will probably get a lot of signers - and perhaps lose your fountain pen.