How should a beginner start strength training after 40?

Nikkiey explains on Ep. 337 that walking, Pilates and yoga are great, but on their own they aren't enough to prevent muscle loss. Picking up dumbbells or a barbell gives your body the stimulus it needs to build and protect muscle. You don't need to chase one-rep maxes. Choose a weight where the last three reps of a set are hard but you aren't throwing the weight around or risking injury.

On Ep. 217, coach Andrea Simulis adds that any movement you'll do consistently is a good start, even a group class. You can change how you train later.

The episodes add some nuance on how much to plan. On Ep. 235, Nikkiey says clarity comes from taking action. She found a back workout on Pinterest and looked up each move on YouTube, sometimes right before doing it. On Ep. 72, she says winging it and random Pinterest workouts were when she felt most insecure. She kept repeating the same few exercises and didn't progress. Her advice is to know your workout, exercises and form before you walk in. When she had a coach, she looked up each exercise the night before. She doesn't recommend watching videos mid-workout because it eats into your rest time.

So don't wait for the perfect program, but don't wing it forever either. A written plan, or a coach who programs for you, is what moves you forward.