Lots of great advice here. I'd add that the position of thermals can sometimes be deduced. There are broadly speaking two types, so-called "blue thermals" where there's no cumiliform cloud above - with these it's merely a matter of luck running into one, recognising the uncommanded roll out of the thermal, and rolling in the opposite direction to commence "centering". Mostly, however, thermals are inferable if they have cumulus above. If you draw a line into wind from the base of the cumulus to your position over the ground, you will generally find a thermal upwind of that line. A really strong thermal may result in a lighter colour area in the centre of the base of the cumulus.
From an RC point of view, timing of the launch is going to be absolutely critical, as if you launch too early, or too late, you'll be launching into "sink". If you're flying within 10 miles of a coastline, the stronger the thermal activity, the more likely a sea-breeze will kill the thermals stone-dead. *I was once one of 17 gliders than all landed at the same field within a few minutes when just sea-breeze occurred. Amazingly we all missed each other on what became a very challenging landing for later gliders.