You -> VPN/SSH -> Tor
You can route Tor through VPN/SSH services. That might prevent your ISP etc from seeing that you're using Tor (VPN/SSH Fingerprinting below. On one hand, VPNs are more popular than Tor, so you won't stand out as much, on the other hand, in some countries replacing an encrypted Tor connection with an encrypted VPN or SSH connection, will be suspicious as well. SSH tunnels are not so popular.
Once the VPN client has connected, the VPN tunnel will be the machine's default Internet connection, and TBB (Tor Browser Bundle) (or Tor client) will route through it.
This can be a fine idea, assuming your VPN/SSH provider's network is in fact sufficiently safer than your own network.
Another advantage here is that it prevents Tor from seeing who you are behind the VPN/SSH. So if somebody does manage to break Tor and learn the IP address your traffic is coming from, but your VPN/SSH was actually following through on their promises (they won't watch, they won't remember, and they will somehow magically make it so nobody else is watching either), then you'll be better off.
You -> Tor -> VPN/SSH
You can also route VPN/SSH services through Tor. That hides and secures your Internet activity from Tor exit nodes. Although you are exposed to VPN/SSH exit nodes, you at least get to choose them. If you're using VPN/SSHs in this way, you'll want to pay for them anonymously (cash in the mail [beware of your fingerprint and printer fingerprint], Liberty Reserve, well-laundered Bitcoin, etc).
However, you can't readily do this without using virtual machines. And you'll need to use TCP mode for the VPNs (to route through Tor). In our experience, establishing VPN connections through Tor is chancy, and requires much tweaking.
Even if you pay for them anonymously, you're making a bottleneck where all your traffic goes -- the VPN/SSH can build a profile of everything you do, and over time that will probably be really dangerous.
You -> your own (local) VPN server -> Tor
This is different from above. You do not have to pay a VPN provider here as you host your own local VPN server. This won't protect you from your ISP of seeing you connect to Tor and this also won't protect you from spying Tor exit servers.
This is done to enforce, that all your traffic routes through Tor without any leaks. Further read: TorVPN. If you want this, it may unnecessary to use VPN, a simple Tor-Gateway may be easier, for example Whonix.