Kirsteen owns shares of GlaxoSmithKline. The Motley Fool UK owns shares of and has recommended GlaxoSmithKline. The Motley Fool UK has recommended AstraZeneca and Tesco. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors. Click here to claim your copy now — and we’ll tell you the name of this Top US Share… free of charge! Renowned stock-picker Mark Rogers and his analyst team at The Motley Fool UK have named 6 shares that they believe UK investors should consider buying NOW.So if you’re looking for more stock ideas to try and best position your portfolio today, then it might be a good day for you. Because we’re offering a full 33% off your first year of membership to our flagship share-tipping service, backed by our ‘no quibbles’ 30-day subscription fee refund guarantee. Simply click below to discover how you can take advantage of this. Coronavirus sparks market volatility! Should you buy FTSE 100 stocks or wait? I’m sure you’ll agree that’s quite the statement from Motley Fool Co-Founder Tom Gardner.But since our US analyst team first recommended shares in this unique tech stock back in 2016, the value has soared.What’s more, we firmly believe there’s still plenty of upside in its future. In fact, even throughout the current coronavirus crisis, its performance has been beating Wall St expectations.And right now, we’re giving you a chance to discover exactly what has got our analysts all fired up about this niche industry phenomenon, in our FREE special report, A Top US Share From The Motley Fool. Our 6 ‘Best Buys Now’ Shares Kirsteen Mackay | Thursday, 19th March, 2020 Image source: Getty Images. “This Stock Could Be Like Buying Amazon in 1997” The FTSE 100 has endured a volatile few weeks. It’s fallen from 7,436 points on February 20 to a low of 4,960 at the time of writing.Billionaire investor Warren Buffett likes to be greedy when others are fearful. Meaning a stage of high volatility and crashing prices is the perfect opportunity to pick up bargain stocks that can create fortunes in the years to come.5G is here – and shares of this ‘sleeping giant’ could be a great way for you to potentially profit!According to one leading industry firm, the 5G boom could create a global industry worth US$12.3 TRILLION out of thin air…And if you click here we’ll show you something that could be key to unlocking 5G’s full potential…This is good advice in ordinary financial crashes, but the trouble is, the Covid-19 outbreak is no ordinary situation. It’s an unquantifiable threat, which makes it very difficult for financial experts to predict the bottom of the crash.Index volatility continuesTaking a pragmatic look at it, governments want to protect their economies, and companies want to survive. Governments around the world have already pledged to inject billions into those economies to help them ride out the storm.So far it hasn’t been enough to stop markets from tanking, but that’s because news of the virus is still filtering through and fear is gripping nations. Much of the volatility is generated by computer algorithms programmed to react a certain way to market changes, further impacting the situation.Uncertainty is rife, and it’s likely that some companies won’t survive the turmoil. However, I’m sure many will and given time, they’ll come back stronger.That’s why, if you’re a long-term investor, I think it’s important not to sell out too soon. Those shareholders who stay invested usually benefit more than those who don’t.This may not be the bottom of the market crash and it could take years for the FTSE 100 to return to previous highs, but this doesn’t mean it’s a bad time to buy.Some of legendary investor Warren Buffett’s key buying criteria include:Choosing an established companyAvoiding business with high debtSeeking dividendsLow price-to-earnings ratio (P/E)Growth potentialFTSE 100 stocks worth watchingThe FTSE 100 comprises well-established companies with a high net worth and is generally considered a wise place to invest.Debt is the next factor worth scrutiny. If a company has high debt, then it faces a higher risk of failure. With the coronavirus crisis gathering pace, this has never been more true. Tate & Lyle produces the ingredients for many foodstuffs, with a particular focus on sugar alternatives and calorie reduction. It has moderate debt and a dividend yield of 5%. So far it hasn’t experienced significant production or shipment issues related to the virus, but is monitoring the situation. With the global obesity crisis continuing, I think demand for calorie reduction ingredients is likely to continue to grow.However, there will always be exceptions to the debt rule. Supermarkets, Tesco, Morrisons and Sainsbury’s are each saddled with high levels of debt but are likely to continue to thrive as demand for their products continues.Each of them also offers dividend yields around 4% and their forward P/E has fallen closer to bargain territory.Drugmakers AstraZeneca and GlaxoSmithKline have high debt but could be considered defensive plays with the spotlight now on global health.I think there’s worse to come, but that doesn’t mean you should wait to buy all FTSE 100 stocks. Providing you’re buying a quality business and are willing to be in it for the long haul, then the price you pay shouldn’t matter as much as it might seem at the time. 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