Supposing that I "believe" in one particular company, but I'm worried that the stock market may be in a bubble overall.
How can I invest accordingly? How can I invest in one particular company, while remaining market-neutral overall?
You can employ a hedging strategy using short selling, put options, or other methods that will partially neutralize your exposure to the overall market.
e.g. You could short sell a market-wide index such as the S&P500, while going long (buying) the company you are interested in.
Investopedia has a nice primer on this:
Also, see this related question here:
For the type of market neutrality you desire, free from crash risk, it's best to hedge the shares with covered calls when implied volatility is expensive and puts when implied volatility is cheap with the nearest at the money expirations. A put only strategy can be very expensive and should only be used with the longest term options available since they can cost many tens of % per year.
Securities become almost perfectly correlated during a crash; therefore, market crash risk of one security is essentially equal to the market crash risk, so hedging the security itself makes a position market neutral for crash risk.
This strategy will have intermittent opportunity cost risk in the form of slower returns during market expansion to pay for smaller losses during a crash; however, the expected long run return hedged this way should be greater than the underlying's expected long run return with less volatility.