I mean I know the 777 is hard to slow down during decent so I slow down rather early. If the speed increase is “uncontrollable” at Idle thrust with speed brakes I would just pitch up or slow down the decent rate.
And for climbing I do about 3000ft/min and pitch for that, or you can just use Autothrottle to stay at 250kts.
I’d say just slow down earlier for descent. And for climbing, with a fixed thrust setting, pitch for the speed, or for me I prefer to use auto throttle.
So for descent, you need to start slowing down earlier. Make sure that you are following the descent pattern of your STAR. If you are not using a STAR, make sure you start your descent early enough. If you wait until you are 25nm from the airport to start descending, the aircraft won’t be able to slow down because you will be descending at such a high rate.
And remember, if you are crossing 12,000 feet and are still doing 300kts indicated, you will likely not be able to slow down in time. Go ahead and level off for a minute or two and let your speed come down. This will help to avoid getting overspeed violations.
As for takeoff, while using auto-throttle is the easiest way to keep you from overspeeding on the ascent, you should be proactive during your takeoff and ascent to make sure you do not exceed the 250kts limit. Remember, you don’t just set the throttle and forget it. You should adjust your speed and AOA to meet your desired climb profile.
Reduce your throttle earlier and your descent rate. If you’re descending greater than 2000ft/min you’re likely to end up overspeeding below 10,000ft
Reduce your throttle. You don’t have to stay 70% if you are speeding up beyond 260kts