What can I do to defend myself against a speeding ticket?

I received a speeding ticket for going 51 mph in a 35 mph zone in Bexar county San Antonio on September 11, 2015 at IH 10 W access road at its intersection with Fresno Street. I was driving with my friend who was in the car with me and had just gotten off the highway and didn't notice the speed limit sign and assumed the speed limit was around 45-55 mph (most speed limits on access roads next to highways are 55 mph in San Antonio.) I had already made a safe and complete stop at a red light when a police officer who was on the road to the right of me ( I hadn't even passed him when I stopped at the red light) put his lights on and asked me to pull over which i fully complied at the time neither me nor my friend knew why we were being pulled over. He gave me a ticket for speeding and we were on our way.

I believe giving me a ticket was unreasonable because i had already made a safe and complete stop when he put his lights on and pulled me over also that I was slowing down
Added (1). I was slowing down to comply with the speeding limit prior to him pulling me over. So long story short i believe i was complying to the law to the best of my knowledge and ability while keeping everyone around me as safe as possible and so I don't believe i should be ticketed?

I pleaded not guilty and will be be set to trial by jury. What can I do and say to defend myself? My friend who I was driving with will come with me to the trial so perhaps he be a witness?

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