When you fly cross country you need a plan.
Your task may be very specific, like a badge or contest task, or it may be fairly general. To set a task you must first be clear about what you are trying to achieve.
As you fly your task, you need to continually reassess your position.
When you are considering whether you can glide to the lift ahead, or to the safe landing option, there are some rules of thumb to help.
1,000ft loss of height per 10km is approx a 32:1 glide.
For a 20:1 glide, use 1,500ft per 10km.
If you know the speed your glider achieves these glide ratios, you can quickly guess the height required to cross a gap, reach the next cloud, or reach your landing ahead.
On a 1:250,000 map, 10km is 4cm. Carry a small ruler for measuring distances on the fly.
If you have a GPS navigation system, learn how to use it to assess those glides.
Always have Plan B. The more options you have, the better off you are.