I love using dildos, and have several toys of different sizes and shapes. My favorite dildo is a 7" cock with balls, and it has a suction cup. It fits me very well, not too large but big enough that you definitely feel it and it hits the right spots. I also have a cordless vibrating butt plug, it has 3 knobs in it, from smaller to larger, and then a wide base so it won't get lost up my ass (which the thought of terrifies me, lol). Sometimes I'll put the plug in my ass and then jack off, often changing the tempo of the vibrations. But when I really want to fuck myself, I use the dildo and go at it if different positions, my favorite is sitting on it and bouncing.

My advice is to start somewhat small, use plenty of lube and go slowly at first. As you get used to it you'll figure out what you really like. I think anal stimulation is amazing and I enjoy it more and more. You really don't need to worry about stretching out your butthole, unless you really plan on using huge dildos...

Main thing, have fun and enjoy!