I am no expert in this, but here are some useful suggestions I have culled from my reading.
Form letters are less effective. After seeing the first one or two, recipients will just ignore the rest.
Congressmen and Senators and state legislators are less interested in hearing from people who are not in their districts. So bear that in mind when you contact them.
Gmail and Hotmail will not reveal your location through your IP address, but many other email programs will.
Direct dialing Congressional and Senate offices will often reveal your location, but using the central congressional switchboards will supposedly not. You can also set your telephone to not reveal your originating number. There are many toll free numbers for reaching the Congressional switchboard. For example, a quick search turned up:
The name of the game in lobbying is irritation and impact. The more staff time it takes to deal with our contact efforts, the more aware our elected officials will be that we are concerned. And the more concern that is expressed, the more nervous these elected officials will be that they will lose their positions, replete with power and perks, if they do not respond to us appropriately.
So how do we have an impact? Email is easily blocked or deleted, but can be sent out in immense volumes, and with great frequency. If you have the option of requesting a response in your email, you should do so. This will force someone to expend effort and energy to deal with your message, and therefore have more of an impact. Faxes and snail mail occupy space and consume time and effort and resources. Phone calls draw on staff resources. The advantage of telephone calls is that they often can produce more useful feedback of the effectiveness of our efforts than other contact methods.
Therefore, I would guess that emails are not as effective as faxes, which are less effective than snail mail, which is less effective than certified letters. Telephone calls are also pretty effective, but I am not sure how they compare to regular physical mail.
Email attachments are often never opened. Email with attachments is sometimes discarded because attachments often contain viruses. Embed any attachments in the body of the email if possible. Gmail allows one to place images in the email body quite easily, for example.
Many elected officials are starting to use web-based tools to cut down on email spam. Looking at the source code of these webpages with email forms can sometimes reveal the true email address of the intended recipient. However, many of these emails sent from these sorts of tools are filtered to reject those that are outside the legislator's district. Even regular email to a legislator's office can go through a similar filter. Bear that in mind when you use these web-based tools. Many of the aides and staff of these legislators, who are often quite influential, still have regular email addresses and so can be contacted by conventional bulk email.
Shorter email messages and letters are typically better because there is a greater chance they will be read.
Placing a long list of email addresses in the "To" slot in your email program is not helpful. An email obviously sent to a long list of people might be discarded automatically as spam in some cases. Even if the software does not reject this sort of email, people receiving such an email might ignore it as spam. If they do read it, they will feel more comfortable ignoring the issues raised since they believe that surely someone else on this huge list will tend to the problem. Therefore, put any long list of email addresses in the "bcc" slot in your email program, and mail the message to yourself. That way the recipients will not know how many are on your email list and what their addresses are. Some email software is designed for bulk emailing and will do this automatically for you.