Excerpted from Soaring Beyond the Basics, page 12.

It’s good to be familiar with how an individual glider handles in center of gravity configurations unusual to you. Think beforehand about how CG relates to launch, gliding, stalling, turning, and landing. This is especially important in multi-place ships. If there is doubt once you’re aloft, test your craft’s slow speed handling at safe altitude to avoid unwelcome surprises later.  

And take the problem of density altitude seriously. Flying from (or into) a field at high elevation, especially if the day is hot, aerodynamic performance is impaired in every way. Takeoff and landing rolls will be longer at high density altitudes, and climbs on tow slower. Also, because actual velocities are greater for a given indicated airspeed, turns will consume more space. You’ll need more room to complete any maneuver when soaring near high terrain, or turning into a tight landing at high elevation on a hot day. 

Heat or cold can interfere with pilot judgment, and quickly become safety problems. Anticipate either or both, and prepare thoughtfully. One good way to hedge the bet is to take a jacket you can fold under an elbow or put your arms through and wear backwards. A warm hat and gloves occupy almost no room when not in use, and they can be stuffed nearly anywhere. We all should protect our skin and eyes from direct sunlight; long-term effects of excessive exposure can be very sad. On hot desert days, long sleeves and long pants are cooler than short sleeves and short pants – if the fabric is loose and light, and you don’t expend too much energy. Getting socks damp before takeoff, whether from perspiration, wet grass, or snow, can give you cold feet in flight. And whatever the weather, always wear footgear substantial enough for a possible long hike in the country...

Unsecured objects floating free around the cockpit present serious hazards. Spilled liquids of any kind are a major nuisance, and anything  heavy  such  as a  hand-held  device can suddenly become a dangerous projectile. Very small items can seemingly vanish, causing pointless annoyance for the rest of a flight as you try to find them – or do without them. They could also fall beneath rudder pedals or between the stick and seat pan where they might jam the controls. (I once saw my tow pilot very nearly crash on takeoff because a two-inch stub of pencil fell below a floor panel and lodged at the base of his stick!) If you intend to fly with lotsa non-essential crapola, consider wearing a flight suit, or a fishing vest bristling with pockets. 

These concerns also are more important in a two-seat glider with twice as many nooks and crannies, half of which you cannot reach in flight. Never take off solo in a two-seater without an aft cockpit check: its controls free and clear, cushions and belts secure, and canopy locked.