Either it's due to your mod's or the server host. If you have a really bad graphics card, it won't be compatiable for higher mod's, and lately we've been having some trouble with the server lately, due to server crashes and restart's. If you don't have any mod's then it might be the server. Hope i helped.
Try to rotate your computer a bit to make the connection to the router better. Exit every internet-using program except of SAMP while playing (Of course)
Try getting a better internet speed\provider.
Otherwise, nothing to do against it. I lag sometimes aswell.