Upon entering a thermal, the standard rule of thumb says postpone that initial turn three or four seconds to bring you further into the rising air rather than immediately turning away, while also allowing time to decide if the lift is really worth stopping for. Most inexperienced pilots tend to turn for lift too soon even if they do go the correct direction, inadvertently swinging back and away from newfound lift. It’s generally best to wait until the lift peaks before turning. Depending on a thermal’s size, this waiting period could last ten seconds or more. When you’re cruising into the wind, thermals will be rising toward you from ahead on course, making it possible to delay that initial turn indefinitely. If you were to turn too soon you’d immediately be below the rising air and need to move further upwind to rejoin the thermal at a lower altitude. By delaying the turn, just slowing up on course may bring you to the top before you reach ther thermal’s far (windward) side. If you wait too long and fly beyond the lift, a quick reversal will put you right back in it.
When running downwind, it pays to turn sooner to avoid shooting through the lift and beyond it very quickly. If you find that you have turned too soon, you’ll know the lift is right there immediately downwind, while more is rising up from directly below you.
If you’re flying across the wind and find a thermal, but are unsure which side it’s on, turning into the wind by default will result in success more often than not. Here too, the air is rising toward you from the windward direction, so if you turned downwind and didn’t find lift you’ld be descending through sinking air downwind of the thermal – while it continues to rise – and you’d need to fly an upwind leg to relocate lift at some point lower in the thermal itself. But if you mistakenly turn away from the thermal in the windward direction, you will be descending into the airspace from which lower, newer pulses of lift are rising, and simply continuing your circle will probably bring you right back into lift without much loss of altitude or time.