when choosing an investment fund, what do you look for? Is it wise to go for the one with the highest historical performance?
Sounds like you're just starting out. I've been researching funds now for about 5 years as a hobby, so I think I know a little bit, but I'm certainly no expert. I hope this is either for a 403(b)/401(k) or a Roth IRA if you qualify. I would definitely go with no-load index funds if you're new to this. I'd check out T.Row, Vanguard, and Fidelity among others. Last I checked Fidelity had the cheapest index funds for those with at least $10,000 to invest (expense ratio of 0.1), and Vanguard was next (many of their index funds require at least $3000, I believe). Depending on who you go with and your tolerance for risk and time horizon, you could pretty easily put together something reasonable - 100% in a total stock market index fund if you're more aggressive, an 80/20 mix between a total stock market fund an a bond fund if you're more conservative, or a target date fund composed of index funds for one-stop shopping - just make sure the expense ratio for a target date fund is reasonable - some of them definitely are not.
I figure that many US companies do enough business overseas that you could get away with no dedicated international fund and keep things really simple with 1 or 2 funds only. If the OP is just starting out he/she may not be able to meet the Vanguard $3000 minimums or the Fidelity $10,000 minimums to get the 0.1% expense ratio, especially if he/she is investing in multiple funds.
Oh, and here I thought the point of owning firms outside of the US was to provide exposure to equities that may zig when my US equities are zagging, or because there are sometimes better opportunities abroad, or simply because the US doesn't comprise the whole market.