A Self-Invested Personal Pension (SIPP) basically serves as wrapping for investments. It forms a tax efficient tool through which to save for retirement. SIPPS provide individuals with control over their investment portfolio in a way many other pensions do not.
SIPPS involve you developing a strategy. You should probably work on a yearly investing strategy and stick to it. Your choices will be guided by how averse to risk you are, but it is normally wise to mix high-risk investments with lower-risk, income-based products. Don’t forget to diversify across asset classes and geographical areas. In summary you will need to know your stuff and/or use a financial adviser to guide you on strategy.