The best practice for introducing new fitness routines involves a gradual progression to avoid injury and promote adherence. Begin with baseline assessments to tailor the routine to individual abilities and goals. It is vital to incorporate a mix of cardiovascular, strength, and flexibility exercises. Start with shorter durations and lower intensities, gradually increasing as fitness improves. Setting specific, measurable, achievable, relevant, and time-bound (SMART) goals can enhance motivation. Additionally, focus on enjoyable activities to increase the likelihood of staying committed. Regularly reassess and adjust the routine to keep it effective and engaging.