Unlike the English [f] where you touch your top teeth with your bottom lip, the consonant sound in ふ is bilabial - meaning both of your lips are involved, and no teeth. Simply bring your lips close together, as if you were about to whistle, and blow the air through the tight space. This is also different from an [h] sound, because to pronounce [h] you constrict the passage of air at the back of your mouth, practically in your throat. For this Japanese sound, the constriction is in the lip area.

If you know Spanish (or if the word for soccer happens to be the same in Portuguese), ふ has the same pronunciation as fu in futbol. As Asher said, your top teeth should not touch your bottom lip. For English speakers this a rather common problem. If your ふ sounds like the 'foo' in food, then you are not pronouncing it correctly.

like in food

Asher's answer is good. I'd like to add a little bit to it. The modern pronunciation of は・ひ・ふ・へ・ほ is the following. は［ha］・ひ［çi］・ ふ［ɸɯ］・へ［he］・ほ［ho］ ［h］Voiceless glottal fricative　https://en.wikipedia.org/wiki/Voiceless_glottal_fricative ［ç］Voiceless palatal fricative　https://en.wikipedia.org/wiki/Voiceless_palatal_fricative ［ɸ］Voiceless bilabial fricative　https://en.wikipedia.org/wiki/Voiceless_bilabial_fricative は［ha］ ・　　 ・ ・へ［he］ ・ほ［ho］ はな へや ほん (flower) (room) (book) ひゃ［ça］ ・ひ［çi］ ・ひゅ［çɯ］ ・（ひぇ［çe］）・ひょ［ço］ ひゃく　　 ひだり　　 ヒューマニズム 　　　　　　　ひょうじゅんご (hundred)　 (left)　　 　 (humanism)　　　　　　　　　(standard language) ふぁ［ɸa］ ・ふぃ［ɸi］ ・ふ［ɸɯ］ 　　 ・ふぇ［ɸe］ ・ふぉ［ɸo］ ファッション フィーリング ふゆ フェンス　　　フォーク (fashion)　　　(feeling)　　　 (winter)　　　　 (fence)　　　　(folk) The pronunciation of は・ひ・ふ・へ・ほ from 8th century to 11th century is the following. は［ɸa］・ひ［ɸi］・ふ［ɸu］・へ［ɸe］・ほ［ɸo］ Though the consonant except ふ changed, ふ has been keeping the same consonant. The reason is because the shape of the mouth is almost the same between［ɸ］and［u］［ɯ］, I think. ※I wrote about the changes of は・ひ・ふ・へ・ほ on the next page. You can read it. http://www.italki.com/entry/554151

I've only know it to be pronounced as fu. The only reason I can imagine hu being used is with katakana. To be safe use fu. I hope this helps.