I’d ban political parties. Parliament members should be chosen by direct voting. Each candidate (given that he/she could pass various tests, have proper education and has enough working experience at important positions – outside of politics) could apply for a seat in parliament. Then the election system would be to vote for parliament members and president.
Regarding economy I would stimulate local industry and local start up business with decreased taxing regulations.
I would also forbid foreigners to own a land in Serbia.