I think the best way for enhancing and controling gene expression is by adding a strong and specific promoter. This promoter should be able to control the spatial and temporal gene expression. This mean that by this kind of promoter you you can control the time and place that it expressed. You can test such promoters using some promoter testing plasmids such as pJan25 vectors, see attached paper.
Article The pJan25 vector series: An enhancement of the Gateway-comp...
There is a research lab at my university that studies this area and has published a very nice article (attached) on the subject that you might find helpful.