If you have been heavily invested in U.S. stocks, likely your portfolio has performed extremely well of late, particular since Donald Trump's surprising win in the presidential election. Following an initial overnight drop in futures in the early-morning hours on November 9, the markets rocketed upwards once they opened and, more or less, have not stopped since. At their closing prices on March 31, the Dow was up 12.7%, the S&P 500 up 10.4% and the Nasdaq up a whopping 13.8% from their respective closing prices on November 8, 2016.At the same time, while the Nasdaq managed a small gain in March, both the Dow and S&P 500 actually declined slightly for the month. Several market commentators have discussed the stretched valuations in U.S. stocks. Additionally, a combination of increased utilization of technology, aging populations in the developed world, and the rise of globalization point to a high probability of muted returns for the remainder of the year, and indeed possibly several years into the future.Positioning Your PortfolioGiven all of this, how should an investor with a moderate risk profile, and for whom capital preservation must be balanced against the possibility of future returns, manage their portfolio?In a recent note to financial advisors, Vanguard offered some suggestions. While the note did not list exact percentages, I did some extrapolating and came up with the following:As can be seen, diversification is the key. Based on recent strong U.S. returns, domestic stocks are fairly moderately weighted in the portfolio, with foreign stocks assuming a key role. Risk in these areas is managed by an allocation to both domestic and foreign bonds, with a small allocation to TIPS for a little inflation protection, in case growth comes in a little higher than the expectation for 'muted returns.'Suggested ETFsOf course, one easy way to implement an overall portfolio strategy is to use ETFs to do so. These tools allow you to get very precise with your allocations, ensuring diversification while keeping costs low.Domestic Stocks - A simple way to get exposure to the overall U.S. stock market is to select a quality total-market ETF. My favorites are the Vanguard Total Stock Market ETF (VTI), the iShares Core S&P Total U.S. Stock Market ETF (ITOT), and the Schwab U.S. Broad Market ETF (SCHB). All of these ETFs have expense ratios of .05% or less, assets under management (AUM) in the multiple billions of dollars, and even offer commission-free trading depending on your choice of brokerage. Please see this detailed review and comparison if you are interested in diving in a little deeper. If you wish to focus on large-cap stocks, while still getting solid exposure to the U.S. market, you might also consider a top-quality S&P 500 ETF. Foreign Stocks - To venture abroad, your simplest option is to select a quality international total-market ETF. My favorites are the iShares Core MSCI Total International Stock ETF (IXUS), Vanguard FTSE All-World ex-US ETF (VEU), and the Vanguard Total International Stock ETF (VXUS). Again, I offer a nice review and comparison for those who wish to dig a little deeper.Bonds - An easy way to get broad overall coverage of the U.S. and foreign bond markets is via the Vanguard Total Bond Market ETF (BND) and the Vanguard Total International Bond ETF (BNDX). I cover BND here along with a couple of worthy alternates. I have not yet had a chance to do a detailed review of BNDX, but it offers exposure to several countries, with the greatest exposure being to Japan, France, Germany, Italy and the United Kingdom. A majority of the fund’s investments are in sovereign bonds with AA rating or better.TIPS - My recommendation here is the iShares TIPS Bond ETF (TIP). With $23 billion in AUM, it offers a solid basket of TIPS along with great tradeability.Summary and ConclusionWith the U.S. market at or near all-time highs, now is a good time to give a little thought to whether your portfolio is as well diversified as it should be. Given the current level of political and other uncertainty in the world, unless you feel you have a crystal ball as to how this will all play out, it pays to ensure you have built a portfolio that will deal well with a variety of potential future outcomes.What are your thoughts? Please feel free to start the discussion in the comments section below.