planning a route with ridewithgps. What works?

I use ridewithgps in "driving" mode as per Mathemagician's comment.

I find it will put route control points on tiny side roads which you can't actually see when plotting out the coarse route. I've got into the habit of reviewing my plotted route and zooming in on my markers and checking that they're not some side street or bridleway.

Overall, I find it an excellent planning tool with realtime altitude profiling a real plus. Don't know if you've sufferred from this, but it took me months to realise that there are Undo and Redo buttons in the top right corner of this profile, so getting an inadvertant control point added when I just wanted to drag the map around isn't an issue any more!

Strava whilst not perfect, non of the gps mapping are, is good because it plots routes that lots of cyclists have used.  I do a quick plot with strava, then check it for busy A roads, cross check it with a NCN (national cycle route) and further check it on Google Maps using street view if anything looks unusual.  

That is how I'm building my route across the UK for my own Jogle.

buy a paper map or download them and plan your route in advance, write out a pictorial route on a small bit of paper you can keep in a jersey pocket in case you forget whwere you are going.

This is a foolproof system, you'll never run out of battery power or a signal and absolutely will avoid routes you don't want to go down.

I prefer ride with GPS to the others people have mentioned. To check that my route sticks to the road I click the street view icon (the little person) and the roads are highlighted in blue as these have been photographed by Google.

I tend to use strava to find new routes as it’s got the best data for popular routes actually used by cyclists.  

I use plotaroute.com to be able to send the file to my garmin fenix with turn by turn instructions.  I sometimes have to switch from ‘car’ to ‘bike’ or to ‘manual’ when it tries to auto plot to avoid what it thinks is a motorway or trying to send me on bridal paths.  Fairly easy and quick once you used it a couple of times, and free!

If you switch the mode from cycling to driving, that will avoid cycle tracks and bridleways...just be careful it doesn't send you on a motorway or similar. You can check a box for "avoid highways", but I don't know how effective it is- I tend to know most of the roads I want to avoid so I don't need to use the feature. Hope this helps.

It’s only as good as the underlying maps. Google maps seems to be very optimistic in terms of what is navigable by bike.

I use Komoot, you can set preferences and it will tell you if there's any unpaved stuff on a route - and highlight it on the map. Then you can manually adjust the route if needed. I'd say it's selling point for me is the fact that it will find bridlepaths and the like so it might not be ideal, but it's by far and away the best bike-specific nav I've used. It will always seek to route you away from traffic for example. Admittedly on a recent ride that let me do a mile of Strada Bianche chalk down action on my road bike on 25s!

Strava I use.  There is komoot and cycle.travel