I had a memorable evening where, while waiting for the host to finish cooking dinner, a music lecturer took me and another of the host's pupils through 5/8 and 7/8 by limping around the room.
As he explained it, if you liken a regular time signature to walking at an even pace, you can liken irregular time signatures (which is what we call things in 5, 7, 11 etc.) to walking with a limp, thus slightly unevenly. For pieces in 5 it's generally grouped in a group of 2 and a group of 3 within the bar, rather like how a piece in 6/8 is usually grouped in two groups of three.
So you take two steps, one of them being 50% longer than the other - STEP-two STEP-two-three STEP-two STEP-two-three. Or the other way round, sometimes the 3 is the first group (and of course some music swaps over at will - an advantage of notating 5 and 7 in quavers is that you can use beaming to indicate the correct grouping).
7/8 is the same, but there are two one-two groups and one one-two-three group. So you can consider it as an extension of 5/8.
One-two-three One-two One-two
One-two-three Four-five Six-sev'n
Again some music moves the subgroup emphasis around and this is usually indicated by quaver beaming. Also you might find 7 done not as 3+2+2 but as 3+3+1 - but I can only recall seeing that once... in something I wrote. This is all just what's normally done, and you'll always find something to throw you for a loop in any time signature when composers start getting ambitious.
So once you've been limping around the room for a while muttering numbers to yourself and clapping beats, you should be in a position to play some tunes in 5 and 7. If you haven't got any, try writing scales out on 5/8 and 7/8 bars and playing those with the 3+2, 3+2+2 subgroup emphasis included. Or just one note repeatedly, with the emphasis on the One, Four and Six.
Then you need to find some music in 5 and in 7 and listen to it with that awareness of the time signature. Hear where the bars fall, hear how the musicians are dividing the bars up. Mostly ignore any singing, because all the songs I know that are in these time signatures don't really bring it out much in the vocal line and let the instruments deal with it - particularly the drums.
I can't bring many to mind right now though. Lunasa play a tune called Road to Barga which is in 7 and notated at http://thesession.org/tunes/5746 in a way which really shows the way people use beaming to subdivide the bar - this one with a strong idea of 3+4 rather than 3+2+2 in most bars. There's a video on YouTube so you can hear it too
starting at 1:14 (the first part of the set is a different tune in 9/8). Listening to that now I'm definitely put in mind of Phillip limping around the room, as this one has a sense that each bar is stretched out by a quaver, even though every single bar has it in it still feels like an extra bit.
Karine Polwart's Terminal Star is in 7/8, although it's one of those songs where the vocal line sort of feels like it's in something else. The version of that from her album Scribbled In Chalk is particularly worth seeking out because the drums make it far more obvious - the one on Threshold is a lot lighter in instrumentation.
And finally I always have to mention Light Flight by Pentangle, which is in sections - some sections are in 3/4, and the other sections are in alternating bars of 5/8 and 7/8. This is great for feeling how a 7/8 bar can be seen as a 5/8 bar with an extra bit in.