1. Change default Mapnik style
Terrible Mapnik style has to be heavily refreshed or changed. It looks like from '00 years and it deterring people from OSM. We have 2014 and design trends has changed since then. In my opinion MapSurfer style is the best alternative. It's beautiful and renders more tags than Mapnik.
check MapSurfer style here: http://osmapa.pl/#lat=35.68&lon=10.55&z=3&m=ms
2. Unflattening the map
Imagine interactive OSM - you click on a restaurant building or icon and balloon with opening hours, website etc. shows up, you click on a church and balloon with religion, denomination etc. shows up. Today most of the tags are "hidden". There are some services based on OSM which are showing details but they are barely unknown outside OSM community. OSM is a huge database which contains a lot of informations but they are wasted now.
3. Extend thematical maps
On OSM.org we have 3 thematical layers and:
- bike map could be "tourist map" with bike and hiking trails, emphasized tourist attractions like museums, viewpoints, castles etc.
- public transport map could be "public utility map" with public hospitals, schools, offices etc. emphasized
- humanitarian map could be "danger map" with shelters, ruins, military buildings etc.
4. Promote offline OSM for mobiles
I've got Locus with offline OSM on my phone, but I find (unofficial) website with offline OSM maps for download very late. OSM should standardize one extension of offline map filetype for different apps like Locus or OsmAnd and make official website for downloading this maps, linked on OSM.org. Offline OSM is great because you can save money instead pay for internet on your phone, unfortunately I think very few people know about offline OSM possibility.
5. More boldness :)
I'm using OSM since 2012, and changes or updates which I can see are barely visible. More boldness with making OSM better :)