ENTPs and INFJs can be excellent matches because they are both creative free-spirits, and tend to be somewhat eccentric. The two sympathize with each other as rebels against the norm and develop a close friendship out of this. The ENTP is especially valuable in this relationship because of their desire to please, which the oft-depressed INFJ responds well to. The INFJ's value comes from their devoted support of loved ones, which brings healing to the ENTP's (usually hidden) emotional wounds, whose creative ideas are frequently met with criticism and rejection.
The relationship is not without it's problems. For starters, ENTPs and INFJs tend to have opposing personal values. The former values progress, efficiency, and collectivism, whereas the latter values truth-seeking, ideals, and individuality. If the gap between the couple is wide enough, this will cause no end of problems and interpersonal turmoil for them. It's the biggest and most difficult issue that the ENTP/INFJ pairing faces. Another one is the hidden but fierce competitiveness that lurks beneath the surface of these two types. Neither INFJs nor ENTPs are good losers, and when it does happen, they erupt on the inside with bitter fury, beginning to see their partner as an antagonist rather than a companion.
I'm not really sure if there's any advice I could give to ENTP/INFJ couples, since I have never been in a relationship myself. But the universal good idea for relationships is to always put your partner before yourself; never seen a couple fail while doing that.