"A Stitch in Time" is a good maxim to observe when it comes to girths, leathers and bridles too, but when purchasing any of those items the buckles, and in the case of the bridle the hook stud fastenings, deserve particular scrutiny.
Avoid the buckle which is obviously poorly finished with the edges left sharp and the tongues loose and perhaps bent. The former cut into the leather and the latter are likely to prove unreliable. Replace bent or loose hook studs immediately.
Stirrup leathers receive the most wear at the point where they turn through the eye of the stirrup iron. It is for this reason that stirrup leathers are made with the tougher "grain" side (the outside) facing inwards, since the dressing etc. makes it more resistant to friction. A wise precaution is to have leathers shortened every so often so as to move the point of contact with the iron. A better insurance is to replace leathers regularly with best quality new ones.
Buy stirrup irons made from stainless steel, nickel ones are cheaper but are liable to bend or break. If using a conventional pattern iron choose a heavy one big enough to slip off the foot in an emergency but not so big as to allow the whole foot to pass through and become trapped. Always wear boots or heavy shoes rather than flat-soled footwear.
Regular cleaning with a glycerine-based soap and reliable "leather food" preparation is essential if equipment is to be kept soft, supple and serviceable.
When leather is neglected or is subjected to constant immersion in water (particularly hot water) or dried over heat, it becomes brittle and will snap in use.
The fitting of saddlery is as important an aspect of safety as its proper maintenance. Saddles (and bridles, also) which for any reason cause the horse discomfort and inhibit his movement can create an unnecessary stress situation which inevitably leads to a lowering of the safety threshold. To ride safely it is always best to have a new saddle fitted by a reputable saddler and to consult him about any subsequent adjustments to the fitting.