improveHis health has improved dramatically since he started exercising.
get betterThe first part of the book isn't very good but it gets better.
rallyThe team played badly in the first half but rallied in the second.
look upinformalOur financial situation is looking up.
pick upinformalBusiness is really beginning to pick up.
work onYou need to work on your technique.
refineA team of experts spent several months refining the software.
by/in leaps and boundsThe sport's popularity has grown by leaps and bounds in the past decade.