It’s simple but not easy. When you’re building a portfolio for someone else, emotion plays a much smaller role. When you do it for yourself, it’s easy to get caught up in greed or fear and to make mistakes (like putting most of your funds in Tesla, like one DIYer I met).
Make sure that you will actually review your portfolio every six months and not every two weeks or two years. Set clear parameters and objective measures. Decide how long something can lag (or lead) before you make changes. Then stick to your rules. The hardest part of portfolio management is discipline.