If it's actual silicone then it should be non-porous, so a bleach solution or rubbing alcohol can help sterilize the toy. I have tried the EF Toy Cleaner
and it does a good job in helping get anything off the toy. It also potentially can also sterilize the toy but I'm not as familiar with the chemicals they used for this so I stick with rubbing alcohol or a bleach solution. If the toys don't have electrics inside boiling is also an option too. I know for metal/glass toys (another typically non-porous material) people run them through the sanitization setting on their dishwashers.
Making sure the toys are clean is important as you are inserting them inside of you, this is important for any toy. We don't want to introduce bacterial or other biologic that will change the environment internally causing infection or major medical problems.
There is a debate on if you want to do an enema before anal play; however, everything I've read indicates you should not use any high pressure enema options or use any chemical enema solutions (warm water is fine). This can be mostly for personal preference, mind you even with an enema a mess can happen; however, generally it's cleaner than without.
I agree with DancerKittyKat, start slow, relax, and don't push yourself to larger and larger plugs, toys, or anal sex before you are comfortable/ready for it. If you work yourself up slowly and enjoy the sensations as you go you'll enjoy the experience more. I discussed introducing my girlfriend to anal sex in another thread
. I personally enjoy prostate play and have been doing that for nearly 20 years now, I also once got my fist in my butt so I definitely appreciate anal play/taking it slow from a personal level and not just easing my girlfriend into letting me have anal sex with her
Regardless, go slow, use lube, relax, and enjoy! And keep asking questions if you have them.