I've been doing some research about how to stay anonymous on the net, and I was wondering what if you set up for instance your browser, to run through a proxy and then run through Tor? Can I browse safely that way? - I am aware that most things can be cracked, bypassed, exploited, etc. (and we all know the onion routing protocol is not as anonymous as we may think). Also I don't trust VPNs / don't know of any trustworthy.
There is no real qualitative difference between a VPN and a proxy -- the difference is mostly quantitative. An HTTP proxy is a proxy for the HTTP protocol; a VPN is a proxy for TCP/IP and everything that can be conveyed within TCP/IP, including (but not only) HTTP. From an anonymity point of view, the proxy or VPN transfers the traffic that goes through it, and "sees" the source IP address and the data contents. If the data is encrypted (SSL...), the proxy or VPN can still see who talks to who, and the size of the exchanges.
Tor can be conceptually viewed as a randomly selected chain of proxies, with nested layers of encryption so that each proxy sees as little as possible. Adding an extra proxy does not really change the game. Arguably, using a Tor chain with one extra node would be better for anonymity, because, contrary to your manual proxy configuration, that extra node will be randomly selected and an extra nested layer of encryption will be applied.