Tardii guide is perfect but i want add more tips for u!
1-if you wanna find each other in lobby easy; do this : when you load the game bring you're cellphone(d pad up)--go multiplayer--preferences--select all setting to "don't care"
2-you have to kill 5 **different**players in *one* session
3-you have to play rank match
--team death match
4-you need 6 players to its work.when you in the lobby host must choose this setting to make easy for you :
*set duration:1000 money
*re spawn time:1 sec
**other setting no important
*this is important:every body select "different"team(team 1 team 2 team 3 team 4....)
5-everybody come together gamer who want achievement shoot with rocket to 5 players and boooom!
i create session for gta 4 every 10 days so join and get you're all online gs!
!link:Grand Theft Auto IV Sessions
i just want help people because i love GTA 4 multiplayer so much