They regularly dip and rise, first to last (4)
I believe the answer is:
oars
'they regularly dip' is the definition.
(oars dip into water)
'rise first to last' is the wordplay.
'rise' becomes 'ars' (I can't explain this - if you can you should give a lot more credence to this answer).
'first' means one lot of letters go next to another.
'last' says to take the final letters.
The final letter of 'to' is 'o'.
'ars' put after 'o' is 'OARS'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for oars that I've seen before include "Poles to propel a boat" , "Indirectly, they make waves" , "These could make you row" , "Soar with propellors" , "Sculls" .)