Creatinine shouldn't go up with dehydration (although it can do) - so yes, make sure you drink plenty. It can also go up if you exercise a great deal (it's a product of muscle breakdown) - if you are a bit of an exercise nut then take it easy for the week or so before you get a retest and definitely don't push yourself until your muscles ache.
It can also be high if you are generally a larger build (in terms of muscle coverage) - the creatinine of a 90kg bloke is going to be far higher than one of a 52kg little old lady.
The machines can be out by as much as 10% on any given test run (so my husband's creatinine for the panel doctor came back at 170, which is waaay high - he normally runs at around 140 - still too high but not nearly that bad; we got him retested at his "home" lab immediately and it came back happily at 131

) - hence repeating the sample is always a good idea to confirm it's a true high level and not the machine having an off day.
Finally - yes, it can go up in renal disease. It's probably the rarest cause of it being high though and it's unlikely you'd be in significant kidney failure without having a few other symptoms or abnormalities (for a start, your blood pressure would be high if your kidneys were failing enough to push your creatinine up).
Don't worry too much about it yet - drink lots, rest your muscles, don't eat too much protein the week before you're tested and good luck with the repeat sample