Hand sewing or machine sewing?
Tbh I'm not the best person to give advice as I tend to just get stuck in, trying to cut fabric and sew with children hanging off me!
But I did do a workshop last week which showed the benefit in cutting things properly ie so fabrics aren't overlapping, pressing seams and taking your time. That's the best piece of advice really, take your time, it pays off (had to unpick so many things!). Pick something that you really want to make as a good incentive. Churning out drawstring bags, while good practice, is v boring!
What are you looking to make?