Johnny, expect a few smart comments on here for asking this question - its part and parcel of posting on pprune!
All I can say is that decent planning is something that comes with time, some people get it quickly, others take longer. I am still setting myself targets whereby I dont want the thrust levers to open from TOD until I put the gear down at 4 miles, nor do I want to have to use speedbrakes to achieve that. It doesn't always work and I've seen myself with Flap 10, Up speed, speedbrakes and maybe gear out if it all went pear shaped or was cut in tight. Nevertheless it is rewarding to get it. The key is that YOU (not the FMC, the path indicator, the banana or anything else) should know where you are on the profile and making sure you fix it. As has been said - If you know you are high and do nothing about it, it will bite you. Sort it out when you are 500ft high, dont wait until you are 2000ft high and being asked to slow down. Similarly, blasting down too quickly and doing 100fpm for 10 miles with flap 5 out isn't really what a CDA is either.
I struggled with this at the start of line training too, for me the key was ignoring the path indicator which has made some far too lazy. I stuck a little post-it sticker over that part of the screen to force me to think about it myself. VNAV, LNAV, Magenta lines, are all great tools - but they are garbage in, garbage out and it WILL lie to you at times. You are flying the airplane.
If you are expecting a 6 mile final, 4 miles out, then 6 miles to where you are downwind then you want to be around 5000ft at the end of the downwind. If you are still doing 250kts, then you need another 5 or so miles at least to slow down. If you have a tailwind you will probably either need to be lower, or use speedbrake which you need to anticipate. If it goes badly wrong, remember you have the gear as an excellent speedbrake. The 3x Altitude never goes wrong. Remember if you have selected a STAR or transition in the FMC it could more than likely be much longer than the radar vectors so will show you low or on profile when you are in fact high. The ND is excellent for "eye balling" a 6 or 7 mile final and the distance you have to get there.
Further up the descent is alot easier to sort out - speed intervention or lvl change depending on your SOPs and 330kts will soon get you back on path! Remember VNAV does this automatically and will move the speed bug down but pitch for the profile but beware of it at high level as it may just hit the barbers pole.
Sorry to ramble on, you will get a million different views from Training captains on this, I would encourage you to do whatever works for you!