Once you set up your NFS exports by adding lines to /etc/exports you need to restart your NFS server; do this with the following:
sudo /etc/init.d/nfs-kernel-server restart
You should see output along the lines of:
* Stopping NFS kernel daemon [ OK ]
* Unexporting directories for NFS kernel daemon… [ OK ]
* Exporting directories for NFS kernel daemon…
exportfs: /etc/exports [1]: Neither ‘subtree_check’ or ‘no_subtree_check’ specified for export “10.1.1.87/24:/nfs/sharedDir”.
Assuming default behaviour (‘no_subtree_check’).
NOTE: this default has changed since nfs-utils version 1.0.x
Assuming no error messages pop up here you should now try to connect to your NFS share.