As crystenah's solution states, you could experience a rise and fall of your guild ranking, depending on the order you choose, but don't lose heart! Your rank really doesn't affect anything in the game if you stick to finishing the quests. You'll be back on track in no time.
First, find Modryn Oreyn in Chorrol for:
"Trolls of Forsaken Mine"
http://www.uesp.net/wiki/Oblivion:Trolls_of_Forsaken_MineNext you can choose Azzan in Anvil for:
"The Stone of St. Alessia"
http://www.uesp.net/wiki/Oblivion:The_Stone_of_St._Alessiaor Burz gro-Khash in Cheydinhal for:
"The Noble's Daughter"
http://www.uesp.net/wiki/Oblivion:The_Noble%27s_Daughterthen
"Mystery at Harlun's Watch"
http://www.uesp.net/wiki/Oblivion:Mystery_at_Harlun%27s_Watc...Whoever's last will advance you.
(Taken from
http://www.uesp.net)