As an investor, I like to invest in companies with proven business models. So it may seem that FTSE100 the index is a natural hunting ground due to the immense number of immense, established companies.

However, even in the FTSE 100, some stocks perform very well and others perform terribly.

Here are some of the things I look for when searching the FTSE 100 for shares to buy.

1. Focus on the future

Companies are promoted to the leading index due to the size of their market capitalization. In some ways this can make the index point rather backwards. Mature industries that are in decline may still be represented, while rapidly growing sectors of the economy may not be represented.

Take tobacco for example.

Power British-American tobacco and rival Imperial Brands be a remnant of a bygone era? Both companies saw revenue decline last year despite forceful pricing power.

2. Sustainability of the business model

National Network is a popular choice among income investors due to its solid dividend and policy designed to boost the dividend in line with inflation.

However, I do not own the shares. Why? I think the business model is less lucrative than you might think. Maintaining it may require more money.

Yes, energy distribution networks are likely to be here for the long haul. However, maintaining or changing them is very capital-intensive. This helps explain why National Grid has diluted shareholders to raise cash this year.

3. Buy business, not gossip

As nationwide companies, FTSE 100 companies often feature in takeover rumors. Buying a company that is then taken over can mean a quick profit.

However, I see this as speculation, not investment. I only invest in a stock because I like its business prospects and current valuation.

4. Always pay attention to pricing

When buying any stock, I think valuation matters – and that applies to the FSTE 100 as well.

To consider Spirax (LSE: SPX), an engineering company that has had an unbroken record of annual dividend growth per share for over half a century.

Business results haven’t been great recently. While revenues reached an all-time high last year, underlying earnings per share fell 18%. Given continued delicate demand in China, I see continued risk for the steam and industrial fluid systems specialist.

But I still think it’s a great company and I’d love to own shares of it. It has a immense addressable market, proprietary technology, a immense customer base, and a forceful reputation.

But is a share of the FTSE 100, which is down 36% this year, worth more than 20 times earnings?

I don’t think so, that’s why I don’t buy it.

5. Consider what makes the company stand out

As with any stock, I look for competitive advantages that I believe will facilitate set the company apart from its rivals.

FTSE 100 companies like it Haleon AND Unilever they have portfolios of unique brands that give them pricing power.

Billionaire investor Warren Buffett, who tried to buy all of Unilever in 2017, is always looking for a company that could have “moat”, which helps him fend off his rivals.