When I first started using plugs, I found lying on my side was the best way. It means I was quite relaxed, and could easily reach round. I started with something a similar size to the one you've bought, but quickly graduated!
My main advice? Lube, lube, lube! Tease with a finger or two first just to get warmed up.
After my first small plug I moved on to a gorgeous smooth glass plug, one of my favourite putchases ever. I didn't get in at LH as it was in a sale in a local sex shop, but it is very similar to this:
the smoothness really helps with getting used to the slightly larger size, and the weight means it feels entirely different to plastic/jelly/silicone - in a good way!!
Hope that helps :)