1) You don't drive looking in the rear view mirror, why invest that way?
Don't become a performance chaser. The notion of a fund or ETF continuing to go up just because it's been up in the past is flawed.
2) Don't get fooled by sucker rallies
Japan experienced a handful of 30%+ counter trend rallies
which resulted in eventual lower lows.
3) Know your numbers
if you've lost 40% you need to pocket a 66% gain just to get even.
4) Don't fight the tape
A look at the Dow Jones and S&P 500 charts clearly shows that investors don't want to own stocks right now.
5) Use common sense
Unfortunately, common sense is not so common. You can't force a winning portfolio. All boats sink with the tide. If you don't want your boat to sink, pull it on shore and wait for the tide to come back. You can park your money in short term Treasuries,