I went on one of Sams trips last year. If you can get into Mitiga (HLLM) rather than Tripoli International (HLLT) life will be much easier for you. It's also closer to the city centre if that's where you are going.
At HLLT getting avgas is a bit of performance. You need to find the fuel company, tell them how much you want and get an invoice for it. Then go into the terminal pay your invoice and bring it back out. Back to the fuel company and then they will fuel the aeroplane.
ATC on arrival was quite busy, but on departure dead quiet.
We had an agent to get us through immigration etc., I don't know if that is compulsory.
If you can get him Sam will tell you everything you need to know.