Senate

locate your Senator (but the Texans are below) - http://www.senate.gov/general/contact_information/senators_cfm.cfm

Texas: John Cornyn

send an e-mail
 - http://cornyn.senate.gov/public/index.cfm?FuseAction=Contact.ContactForm

write a letter -

John Cornyn
517 Hart Senate Office Bldg.

Washington, DC 20510

Main: 202-224-2934
Fax: 202-228-2856

John Cornyn

5300 Memorial Drive

Suite 980

Houston, TX 77007

Main: 713-572-3337
Fax: 713-572-3777

Texas: Kay Bailey Hutchison

send an e-mail - http://hutchison.senate.gov/contact.cfm

write a letter -

Kay Bailey Hutchison
284 Russell Senate Office Building

Washington, DC 20510-4304

202-224-5922

202-224-0776 (FAX)
202-224-5903 (TDD)

Kay Bailey Hutchison

1919 Smith Street
Suite 800

Houston, Texas 77002

713-653-3456
713-209-3459 (FAX)

House

DIY search: http://en.wikipedia.org/wiki/List_of_United_States_congressional_districts#Texas

1. figure out your district from the map
2. click the district link
find the representative's name on the wikipedia article
3. skim their bio and find their official site at the references/external link section at the bottom of their wikipedia article
4. find the contact form section of their website and send a message to them.

Find your district representative by zip code -

1. the four numbers after your 5 digit zip: http://zip4.usps.com/zip4/welcome.jsp
2. find your district rep: https://writerep.house.gov/writerep/welcome.shtml
3. write them a letter

Helpful instructions from http://www.essortment.com/all/writeyourcongr_rcem.htm:

Include your address and phone number, the date, their address and a salutation something like the following: To the honorable Senator First M. Last. Now reference the topic including any specifics about bills or issues by their specific numbers or however they are known.

In the body of your letter make it clear what you know about the topic, what you know about your congressman’s involvement with that issue, what you want and what you will do politically to get it. ... You will be most effective if you come right out and politely but clearly tell your congressman that if they want your vote in the next election they should vote the way you are asking them to on that particular issue. This makes it very certain where you stand and that you are serious.

You can write about several issues in one letter but may find it more effective to write a separate letter on each issue. If you have any genuine political influence yourself you may want to find a way of making it known as well. ... Sign and date the letter.