Another option is to pick the files and folders you want to sync with your cloud service and move those into the cloud sync folder, leaving older or less useful files on your PC (you can use the fetch option in SkyDrive to grab files from another PC remotely as long as you leave your PC on). You can do that with two Explorer Windows by drag and dropping, but if you’re going to do it a lot you can save time by adding links to your cloud sync folder to the Send To context menu that you see when you right click in Explorer.
Open your user folder in Explorer; you can navigate there by opening your C: drive and looking for the Users folder and then your name, or you can type %UserProfile% into the address bar. This is where you’ll find the icons for SkyDrive and Google drive; if your Dropbox folder is elsewhere, open that folder. Now open the SendTo folder in another Explorer window. Depending on your settings, you might see a shortcut to it in your user folder. If not, type shell:sendto into the address bar of an Explorer window (or into the Run dialog which you can open with Windows-R).
Make a shortcut to the cloud sync service and drag it into the SendTo folder
Right-click on the icon for the cloud sync service you want a SendTo entry for and choose Create shortcut. Drag the shortcut into the SendTo window; if you want to you can rename it to remove the word Shortcut. That will put an entry in the context menu for the service, and you can have one for each service.
The disadvantage of this method is that it copies the files and folders you use it with into the root folder of your cloud storage; if you want to keep it organised into a few higher level folders like Documents and Photos, you can add SendTo links for each of those as well. Just open the cloud sync folder, make shortcuts the folders you want to copy files into and drag those into the SendTo folder.
Use the icon for your cloud service to help the link stand out
You’ll definitely want to change the names of those shortcuts to make it clearer where they point to. While you’re at it, you can add the correct icon for the shortcut. Right-click and choose Properties then click Change Icon on the Shortcut tab. Browse to the Program files folder and pick the EXE file for your cloud sync tool; Explorer will grab the icon and show it.
Create as many SendTo links as you want for your different cloud folders