Tips and Help with Soldering
The goal of tinning is to leave a very thin, uniform coat of solder on the wire. So.

1 You will be manipulating 3 objects simulataneously: wire, solder and iron. As you've undoubtedly noticed, you only have 2 hands. So you'll need to immobilize one of them. I suggest the wire. You can get various nifty bench vises to hold pieces in place, but a good field expedient is a thick book. A dictionary will do nicely. Put it on your work bench, and put the wire about halfway through the book, with about an inch or so of wire (with the bare end exposed) showing. For tinning, the wire should be facing toward your dominant hand (usually the right). You'll see why later.

2 Don't use thick solder. .050 is good general-purpose, through-hole solder. Save the really fine .025 for surface mount work. And use rosin-core solder, too. 

3 For tinning, set the iron to maximum temperature unless you're using really cheap wire with insulation which melts easily.

4 Clean the iron tip, then touch solder to the tip. You don't want a hanging blob, just a slight bulge of solder.

5 (Assuming you're right-handed) hold the iron in your right hand and the solder in your left. Touch the tip to the exposed wire near the insulation. The solder on the tip should make contact with the bare wire, and a bit of solder should  bridge the gap between tip and copper. Now, simultaneously move the tip toward the end of the wire, and at the same time feed solder into the junction of tip  and wire. The tip rate should be rather quick, and you can see the solder spread over the wire. At the same time, move the solder along with the iron, looking to see how much solder is being melted and tinning the wire. This does take a bit of practice, but if you're getting a blob you know you're adding too much solder.

6 It's easy to feed the solder onto the iron tip. Don't. The solder should contact the material being tinned. If the tip is properly tinned, there will be good thermal contact between the tip and the wire, and the best point to aim for is the junction of tip and wire. This way, even if the wire surface is dirty, the heat of the tip will activate the rosin core and clean the joint.