Some beginners are unhappy with the look of their solder lines. While there are many products available to make your soldering easier, the short answer for obtaining smooth, consistent solder lines is practice, practice, practice.
As you practice you will learn what products work for you. while 60/40 solder (60% tin/40% lead) is the most recommended alloy due to a low melting point, you may find that a different alloy gives you a better result.
The typical soldering iron produces more that enough heat to melt your solder, so you will probably want to use a temperature controller. Some soldering irons are available with built-in controllers . Modern stained glass irons have iron clad tips that eliminate the need to frequently file the soldering tip. Just wipe the hot tip on a block of sal-ammoniac to clean.
A thin coating of Anti-Sieze on the soldering iron tip will keep it from 'freezing' into the shaft when it is time to replace the tip. Use a touch of Anti-Sieze on the locking collar, or screw, as well.
Different size tups are available for fine detailed decorative soldering versus large window panels.
Again, your choice or flux is a personal preference. The fluxes we stock all do a fine job of chemically cleaning copper foil and lead or zinc came before soldering.
Finally, a picture is worth a thousand words. If you are still unhappy with your soldering, take a look at a DVD such as Vicki Payne's Professional Soldering. Watch with close up camera angles how easy it is to improve your soldering.