What about it is it that you're having problems with? Sending/receiving data is really easy with Lidgren. Figuring out what data to send and how to actually read/write that data from/to your entities is something that no solution will free you from, except possibly using an existing engine..
How much stuff do you need to synchronize? tens, hundreds or thousands of entities? If it's ten or so, then you can probably get away with sending everything all the time. If it's on the scale of hundreds or even thousands, then you'll need to figure out what to send to which player at each given time.
In each map there will be about from 50 to 200 entities (the maximum supported entities is 65536, a ushort) for a max of 24 CCU, and for each entity I have to send 7 data parts: position, rotation, scale, velocity, color, texture index and render depth, plus the entity unique ID.
My problem is that I know how to send/receive packets with Lidgren, but I don't know how to store and read them in an efficient way to do lag compensation and input prediction.
In fact, I'm very noob at game networking. I read numerous times the Source Multiplayer Networking, but I still don't understand it completely.