For the B747-400 you intially burn 10-11 tonnes per hour in the cruise and the optimum altitude increases approx 1000ft per 10 tonnes burnt. So in NAT OTS you may ideally climb each hour (although in practise about each two hours).
In normal rvsm airspace, with 2000ft between levels in the same direction, it would be less frequent, although in either scenario, and subject to weather/turbulence predictions, sometimes you will decide to fly above optimum and close to maximum if you feel you may not 'get' the altitude later on.
It's all a game of strategy, just like coming out of Singapore pre-rvsm, when you may be offered FL240/260 (rather than your preferred FL310) or a 30 minute delay. You burn lots of fuel down at FL240 (which you may have to stay at until India) but will make it back up later on (or most of it with the RB211's) when you climb straight up to FL340/380 for the last 7 hours of flight.