At the moment I'm trying to learn Them Bones by Alice in Chains but I'm having trouble playing in time as its in a fairly unusual time signature (I think it's 7/8), any tips?
When I deal with odd time, I split the notes in to two groups or three groups.

For 7/8, you could split the notes in to two groups: 1 group of 4, and 1 of 3, or vice versa. So you'd tap your foot only twice for one bar of 7/8. 123 1234 or 1234 123.

or you could do 3 groups, so you'd "feel" the bar in "3" (3 taps of the foot). 12 12 123 or 123 12 12, or 12 123 12
Last edited by mdc at Mar 4, 2012,

And for any difficult rhythms: SUBDIVIDE

. . . Subdivision is the answer to everything, especially playing strange rhythms in odd time signatures
Them Bones would be 12 12 123. I play a lot in some weird ass time signatures, but i fined it is best to not think about it when you are playing. Focus on the riff or the melody.

Pretty straightforward just play the 1 then its straight eighth notes from 2 to 7.

When you are counting seven make sure its Sev..not Se ven.
A song like this, you don't really need to get too technical with the counting - it's a pretty easy thing to feel in this context.

But the above advice is sound if you're finding yourself having trouble.
mdc already gave good advice, but I would like to state that "feeling" complicated time signatures most probably won't work out if you aren't very used to them. Most of the time 7/8 is counted like 1-2-1-2-1-2-3. One thing to try is to tap your foot on every "1". This should get you used to this kind of time signatures. You can subdivide any time signature in groups of 2 and 3. So I really suggest you count it somehow.