Short answer: value investing, the investing process espoused by Warren Buffett, Benjamin Graham, Seth Klarman, Joel Greenblatt, Bruce Greenwald, Bruce Berkowitz, Charlie Munger, and generally a disproportionate number of great investors. 

Slightly long answer:
Depends what you mean by "short-term" gains.  I think you mean how do you maximize growth over a 5 year period as opposed to booking short-term gains over and over again (e.g. every 3-6 months) over 5 years. 

If I have the interpretation correct, then value investing is the way to go given that you actually have what's considered a long-term time horizon in the investment world (2-5 years).  Most people focus on <2 years (most hedge funds, traders, and even many large asset management firms). 

The overarching theme of value investing is buy assets for significantly less than what they're worth by exploiting market inefficiencies created by institutional constraints, forced selling, fear and greed, and other market/investor irrationalities.  Look at assets that are ignored, unloved, in the dumps, etc.; engage in a thorough analysis of the value of the asset; invest only when there exists a considerable margin of safety (i.e. when you're getting a crazy bargain - 50% discount to intrinsic value); and when you find such an asymmetric risk-reward, bet big (something like 5% of your assets, so that you have a total of ~20 positions). 

It's a simple strategy but a difficult one - which seems to be the case with all good ideas (that is, they are simple but difficult).  You'll have to learn a lot and commit a decent amount of time to the endeavor, but you'll also stand to reap great rewards.  To learn more, look up some of the people I mentioned above and start reading what they've written/said. 

Happy bargain hunting!

I recently started making investments and did a bunch of research on exactly this topic (I am 26).  I also had some friends ask me about what I decided.  So what follows is an edited version of what I told them.  It is a compilation of my personal findings or opinions based on the general consensus of what I researched as applied to my personal situation and preferences.  Your situation and preferences will be different.

Basic Principles:

• Invest in low-cost broad based index funds. Fees and costs have more to do with historical returns than who is making picks. This is because in the end you can't beat the market. So you just invest in the market as a whole.
• Decide on an asset allocation mainly out of two categories: equities/stocks (higher risk/return) and bonds (lower risk/return). You can also throw in commodities such as gold, which have different properties, but it is more nuance than what I want.
• You can also make another decision axis along domestic or foreign stocks. Generally speaking, domestic is seen as lower risk/return while foreign is higher risk/return. But of course that depends on where you are investing it (Europe vs Asia) and how much you believe in Amerikuh!
• Pick a time period and re-balance according to your original allocation. This protects you from doing stupid shit. If your stocks did well, then they'll be a higher percentage of your allocation. Sell some and buy bonds to re-balance, this forces you to stick to the plan and realize some gains.

So for my profile - young, expecting regular income to be steady and increasing, and in it for long term gains - I wanted relatively higher risk/return. So in terms of actual investment strategy what I did was this:

• Stock/Bonds ~ 80/20
• Domestic/Foreign ~ 60/40
• Keep 6 months of living expenses in cash equivalent (savings)
• Set aside some money to spend on fun, and use the rest for this long-term investment
• Invest 90-95% of that amount using the above asset allocation
• Use the remaining amount for vanity stock picks or ones I personally believed in (I bought some AAPL)

A big question for me as I did this research, well so what actual funds fit these profiles.  This is not an endorsement, but I went with Vanguard ETFs (preferred) or mutual funds.  The difference I never fully groked, but I don't think is is too important but its supposed to be lower cost. Here are some of the specific ones I did:

VTI - Vanguard Total Stock Market ETF (US Stocks)
VXUS - Vanguard Total Non-US Stock Market ETF (Foreign stocks)
VBMFX - Vanguard Total Bond Market (US Bonds)

In general, you should just spend some time to figure out your risk profile. Then pick something, do it, and then forget about it (until rebalancing time). It's really not worth stressing or obsessing about it trying to make minute optimizations. This is a low-stress, basic principles strategy.