First and foremost.  You must match the solder to the item.  For ELECTRICAL connections you should select solder with a rosin core flux.  It is commonly found at radio shack.  Most of the time if you use proper solder and a clean iron you will not have a problem with electrical.  Good tips on making sure you tin (pre-solder) the connector and the wire.  Then assemble and then appy heat to the junction and let the solder flow into the connection.  Do not melt the solder on your iron and let it flow to the wire.  That is an improper joint (typically called a cold joint).   Typically in electical if you have a good rosin core solder you will not have to pre-flux anything. 

The same applies for mechanical connections such as servo push rods.  You should NOT use rosin core solder for these joints, you should purchase a good solder designed for metal such as Stay Brite and its accompanying flux.  For these connections you SHOULD use flux before applying heat and solder - even if the solder has a flux core.  You can commonly find the proper solder for metal at Home Depot or Lowes and the accompanying flux.  

A sixty watt iron is plenty for anything electrical outside of huge connectors - certainly more than enough for a deans on which I use about a 30 watt iron.  On pushrods and other metal to metal, some use a small butane torch, but I like a high wattage soldering gun (Weller is a good brand).  My gun has a 100W and a 125W setting....I don't like using open flame on any soldering unless it is plumbing where you may truly need the heat a torch provides....