Playing thirds alternating fingers 24 with fingers 35

[gupiano]

I find it very difficult to play thirds alternating fingers 24 with fingers 35 especially if finger 4 is on a black key and the other fingers are on the white keys. Are there any exercises or advices intended to make it easier or to prepare the firgers for that? It seems that the 4th finger gets stuck between fingers 3 and 5.
Thanks.

[timothy42b]

Play a scale 13, 24, 35, 24, 35, all the way up.  Back down it's 24, 13, 24, 13, 24, 13.

Do that for every major scale.  This is much more efficient than going chromatically and much easier to apply to real music. 

You may have to use smaller increments at first.  13, 24, then back down until learned.  13, 24, 35, and back down until learned.  13, 24, 35, 24, and down.  etc. 

[keyboardclass]

Use your arm when doing them slowly: