I have to admit here, that the second time i played the game, i removed the XP cap and was already as leveled up as one can imagine, plus i cheated and gave myself the best equipment there is. So basically i could kill pretty much everything in the game without any sweat. Not recommended though, it spoils all the suspense in the game, but i already finished it once, the normal way, so i was just a bit fooling around i guess. :D

Enter the beholder lair. Kill the first beholders you see. They got the blood you need so you can take it and exit then return to the mathron mother with it. You can clear the rest of the beholder city later...

Rataxes' advice is the best. Do all three dungeons before you enter the Drow City. You will have as much time for the quests as you want and all quest items (and other special items) will be there even without having any quest. Now, enter the Drow City and store the quest items somewhere in a chest (several chests are on the market place of the city).
Once you enter the Drow City, most of events are timed. When you get the Mother Ardulace quest, you will be able to take the wanted item from your chest and finish the quest immediately.
If you have lost this possibility then try Beholder Lair. It's a difficult dungeon but, as it has been noted above, the Eye is at the very beginning of the dungeon. Catch the eye, leave the lair, and complete the quest. Return to investigate the lair later.