There are a lot of views on this. I don't think there is any right or wrong answer.
I try to keep all holdings at less than 15% of the total portfolio.
I like a mix of both growth and value opportunities. It's hard to classify sometimes and depends on the company.
I also like to add some ETF's to the portfolio to give both international and some targeted exposure. Eg the Nasdaq 100 (NDQ)
I like to initially buy a small holding say with a value of 1% of the portfolio. As my conviction increases I buy more.