Twist Series: Growth & Length Retention II

• While maintaining twists, how can you prevent the ends from getting tangly (scraggly)? 
• i second the question on how to prevent tangly ends while in twists. they feel detangled before i twist them, but when i take them down i sometimes feel the tangles.

I first make sure to twist on damp/dry, stretched hair.  (Shrunken ends are more inclined to tangle than stretched ends.)  To prevent tangling after twisting, I keep moisturizing and washing to a minimum - about weekly or biweekly.  By the end of week #2, my ends are pretty shrunken and this would be a perfect time to redo my twists.  However, I tend to keep twists in for 3-4 weeks at a time.  Slightly tangled ends at this point are almost inevitable, but shea butter or some water + conditioner help the strands separate fairly easily.  (If the ends are really tangled, that may indicate that you're in need of a trim.)

• How often should you trim while wearing twists? 

Trim as often as needed rather than on a set schedule.  (See this post.)  Trimming on a set schedule reduces length retention in my opinion and experience.

• When is the best time to start pinning them up? I'm noticing that I'm losing some length due to damage at the ends, though I've been wearing my hair in twists as a protective style for the past few months.

Ideally, you want to start pinning up twists when they are long enough such that the style is effortless and does not cause much tension on the scalp or ends.  For me, that "comfortable" length was APL stretched.  Damage at the ends can result from a number of sources: pinning up the twists too early, leaving the twists in for too long, impatience during the twist takedown, improperly taking the twists down (i.e., pulling them apart from root to tip = bad), dryness, etc.