My limited understanding - You've 2 choices. A macro lens or macro filters on your existing lens. You're asking a lot of the current lens to expect decent macro without giving it a hand while still taking landscapes.
A macro lens will typically give the best performance and will focus with the lens really close to the subject - expensive though.
Macro filters are cheaper and work well across all zooms and can be stacked for different magnifications. Since they are fitted to a standard lens running in manual or macro AF mode from the body they will typically not focus with the lens as close to the subject as a dedicated lens but will bring the minimum focus distance a lot closer - a LOT cheaper too.
Assuming filters - Don't use the zoom much or at all stay at the wide end and you can move in physically closer with most standard lenses. Don't use AF, focus manually. Use a tripod and a delayed shutter release (timer) a mini one is fine. When stacking filters always make sure that the strongest filter is closest to the lens, the more you stack the more chance of image quality problems from reflected artifacts from all that glass, which isn't coated as well as the components of your lens or gets dirty. I've not had many difficulties stacking my set of 3 and problems can be avoided with careful lighting which you should be doing anyway. Work within the limitations of your lens/camera and be prepared to crop the final image if neccessary you've mega pixels so for the image sizes concerned some loss is ok. Getting close isn't everything some distance from the subject can make lighting a lot easier. Be aware that you lose some depth of field with filters so stop down as much as possible and stay at the wide end of your zoom where your lens will be faster. Also the edges of the image can blur a little,but given that our subject is central in the foreground with a plain background out of focus through short depth of field having this background more out of focus at the edges isn't the end of the world. If you do go for filters buy them from a shop so you can try them out with your camera on a test subject. You'll probably need something over +4 for something as small as a fly +10 might be better. I have this set
Camerafilters.com - Detail and don't find stacking to +7 to be a huge problem I am considering the
Camerafilters.com - Detail though. You'll need the right size for your lens or an adapter ring too. Sorry that those are US links but I'm just rattling this off so they'll do.
A Comparison of Close-up Filters and Macro Lenses - Tim Trott Photography shows the differences quite well. IMO for a SBS you can get good enough results with filters. Depends how flash you are with your cash a macro lens will be fantastic but £100's rather than £10's.
If this was helpful rate me, I want to move on up the road sooo much