Heres what I do....Firstly I have one of those black Jeppesen JAR-FCL logbooks with loads of columns. I fly the A320 and am on a CPL/IR although the ATPL upgrade is fast approaching. I log chock to chocks. All time is logged as multi pilot for obvious reasons. I log all time as IFR as well since that is what we are doing. The logbook has further columns for night and P1 and co-pilot. I am not overly an*l about night time and if its dark I throw in a bit for that. It all helps in the end. Some guys go to the extent of printing out official sunrise/sunset timetables and good on them for being so accurate.
Above the P1 printed column I annotate P1/s or PICUS. For the legs that I am pilot flying (PF) I log the time under the P1/s column. On the remaining legs I log it as co-pilot time. At the end of each sector since I am doing paperwork usually once we are on stand I usually reach down to my nav bag which is beside me and update the logbook there and then or at least get a print out from the MCDU for later in the cruise if things are busy. At the end of the day I will get the captain to sign in the remarks column for me against the legs we flew together.
The best advice I ever got was to keep your logbook current. I regularly fly with guys that haven't updated their logbooks in ages. They then spend literally days with bits of paper updating.