Building a world-class ASX share portfolio in 2025 isn't about chasing the latest trends or speculating on unproven stocks.

Instead, it is about focusing on high-quality businesses, paying a fair price, and holding for the long term.

With the right approach, investors can create a resilient, growth-focused portfolio designed to generate significant wealth over time.

Invest in high-quality ASX shares

A great portfolio starts with owning shares in top-tier companies. These are businesses with strong competitive advantages, solid earnings growth, and a proven track record of delivering for shareholders. On the ASX, two prime examples of such companies are CSL Ltd (ASX: CSL) and ResMed Inc. (ASX: RMD).

CSL is a global biotechnology leader with a dominant position in the blood plasma and vaccine industries. Its long history of innovation and high margins make it a standout in the healthcare sector. While its share price can sometimes look expensive, long-term investors who buy at fair valuations have historically been rewarded.

ResMed, a leader in sleep apnoea and respiratory care, is another high-quality company. With a growing global market and a focus on cutting-edge healthcare technology, ResMed continues to deliver strong earnings and revenue growth.

Holding such ASX shares for the long term can be a winning strategy for investors seeking both capital appreciation and dependable returns.

The importance of diversification

Even the best individual stocks can experience short-term volatility. It is for this reason that diversification is crucial for investors. A well-balanced ASX share portfolio spreads risk across different sectors and industries, reducing exposure to any single company's misfortunes.

One way to achieve diversification is by investing across multiple sectors. For example, in addition to healthcare giants like CSL and ResMed, investors could consider high-quality ASX shares in technology, financials, and consumer staples. This ensures that no single sector dominates their portfolio.

ETFs: A simple way to build a winning portfolio

For those looking to diversify with ease, exchange-traded funds (ETFs) can be a fantastic option. Two standout choices are the BetaShares Nasdaq 100 ETF (ASX: NDQ) and the iShares S&P 500 ETF (ASX: IVV).

NDQ provides exposure to the biggest and most innovative US tech companies, including Apple, Microsoft, and Nvidia. Given the continued growth of the tech sector, this ETF could be a strong performer over the long run.

IVV, on the other hand, tracks the S&P 500 index, offering broad exposure to 500 of the largest US companies. With a mix of high-quality businesses across various industries, it could be a great way to build wealth steadily over time.

Foolish takeaway

The key to building a world-class ASX share portfolio in 2025 is no different to 2024 or every other year.

It is to focus on high-quality companies, buy them at fair valuations, and hold them for the long term. Diversification across sectors and asset classes further strengthens a portfolio, and ASX ETFs like NDQ and IVV offer a simple way to achieve this.

By following these principles, investors can create a portfolio designed to generate wealth and withstand whatever the market throws at it.