The miracle on the 737-800 is that especially when you're new to it you will probably be (assisted by ATC) be high on profile - the key is really to play with the modes, which takes practice and a couple of messed up descents as well just to find out what doesn't work
I for myself calculate a 3° TOD, subtract half a mile for each 10 knots of headwind, add a mile for each 10 knots of tail wind, add a mile for each 10 knots to be slowed down. Gives me a rough idea, but at some airports the MRVAs dictate that ATC will keep you high according to your descent plan, sometimes considerably. Lets assume you don't use VNAV - you could start your descent using V/S at about 2200fpm, speed at 280 - monitor the trend, if the A/T kicks in increase your rate of descent after checking the banana - the great thing about V/S is that the banana will more accurately show you where you will reach the MCP altitude than in LVL CHG (due to the variable vertical speed). If ATC gives you a speed restriction or you reach FL100, change to LVL CHG - monitor the vertical speed trend, if ATC wants you to slow down expect to go high on the descent path - might be a good chance to use the speed brake if necessary. If you level off due to ATC and you don't have a speed restriction, reduce the speed as much as possible (and allowed by the local regulations) to bleed off some energy, once you are cleared to descend don't forget to increase the speed again to resume a high rate of descent if necessary. If you notice you cannot lose energy fast enough, don't hesitate to use the speed brake, if you're within 25NM of the airport consider setting flaps 1 or even 5. If you're able to reduce to 220 knots 5 NM before turning final you're in great shape. If you end up high on the glide path, gear down usually does the trick - speed brake below 230 knots really doesn't do much except shake the airframe.
Hope this helps in some way, best of luck!