Some of the mystery of odd rhythms is removed if you think of them as combinations of blocks of 2 and 3 beats. 5/4 time, for example, can be counted (One Two)(One Two Three), or (One Two Three)(One Two). The 7's have two blocks of 2 beats and one block of 3 beats, for example (One Two)(One Two)(One Two Three), or (One Two)(One Two Three)(One Two), or (One Two Three)(One Two)(One Two).
Another way to look at the odd rhythms is as patterns of short and long counts. The two beat blocks are short, and the three beat blocks are long. Then for the 7's you have short short long, or short long short, or long short short. Experienced players tend to think of odd rhythms in these terms. The key to having good rhythm is to put the rhythm in your body. Your mind may think 12 12 123 12 12 123, but its easier to feel short short long short short long. Also, it's easier to use triplets when you're not thinking One Two, and to use two notes when you're not counting One Two Three.
Here's an example for the 7's with the pattern 12 12 123. Try playing triplets during the 2 beat blocks, and 2 notes during the 3 beat block. That is, play (123)3(123)3(1-2), first while counting 12 12 123, then try it while feeling short short long. It's much easier to do it by feeling the rhythm than by counting it.
One way to put the rhythm in your body is to dance or walk in rhythm. Walk around and stomp your foot on the 1, like stomp step stomp step stomp step step, then starting with your other foot first, stomp step stomp step stomp step step.
A good way to practice playing the 7's is at the same time you practice scales. Major and minor scales have 7 different notes, which lines up nicely with the 7 beats of this rhythm. When you practice scales, don't just play the notes in sequence from bottom to top, top to bottom. Mix up the order. Play each note only once, but play different interval patterns. Synchronizing these scale melodies with odd rhythms can be great practice for improvisation.