I never used to clone but I figured out a way for it to work for me.
The process I usually follow at the start of each season is to develop my next seasons car first to about 45-50%, the whole time I'm spying on the fastest car on track, usually they are high 90s or even a solid 100%. Once I get next seasons car done I switch to this seaons car Dev and clone all the parts I can, you still get some dev on the next seasons car too )even with the slider all the way to the left) so you can start a season with a 60-65% car which makes it easier to Dev the following season.
I continue to spy on the other team as cloning never gets you all the way up in percentage, so I sometimes clone a couple of times each part or dev them enough to catch up. ALways be spying on the best car each race so you have something to clone. If they are not fully dev'ed spy on them again and see if they improve before cloning that part.
