Keeping It Simple (And Short)
Trolling is actually very easy. Apart from your normal casting equipment all you need is a boat. And off you go: let out the lure and drive off. All you need to do now is to catch some fish.
Where And How?
The first questions you'll be asking is where to go and how fast. There's a lot of talk about trolling the open water, but in most (deep) lakes you'll be better of staying close to the shore. You won't usually be as close to the shore as when you cast, but there's always some fish staying a bit away from the shore and the obvious structure. The speed can be quite fast in my experience, the most important thing being that the lures work well at the speed you're going. You shouldn't just go in a bees line at a regular pace. Very successful is to take a rod in hand and actively present the lure with twitches and jerks or slower movements. When you're rowing or fishing with more than one rod you'll have to fix the rods somehow to the boat. There are lot of rod holders for this purpose and they are not all good. If you don't have one you'll find a way of jamming the rod between the boat and a heavy piece of equipment (rucksack, tank, box, anchor, etc), but be careful: the line and the rod blank shouldn't make contact with hard or sharp stuff which could damage them.
Lure And Depth
One of the best lure types for trolling are
plugs (minnows and crankbaits),
but you can use any lure as long as you adjust your speed and take precautions
against line twist (thinking of in line spinners) by mounting an eccentric
weight in front of the lure. The big advantage of plugs is, that their
running depth is quite easy to
predict and control. And there's another important question: how deep should I
troll? Keeping close to the bottom is seldom wrong, especially when you're near
the shore and not deeper than about 10m. But you have to experiment and it's
best to have several lures with different diving depths, although I do have a
tendency to go with rather deep diving ones. But it is very well possible to
catch fish with a lure diving to 4m over 20 or
30m of water and away from the shore.
How Much Line Is Out?
If you want to bring a Plug to a determined depth, you'll have to know how much line you're letting out. I don't have a line counter but do a rough estimate in the following way: while the boat is running I point the rod tip in direction to the lure while blocking the line, then I let the line go and snap the rod backwards until it's in a right angle to the line and then immediately block the line again and slowly point the rod tip back at the lure again. I assume that with every backward pull of the rod I let out about a rods length of line.
The first additional piece of equipment I'd always want when trolling is a fish finder. First of all to avoid snags and to know just how close I can go to a steep shore. Although I have to say that it hasn't always proven very successful to go as close to the shore as the diving depth of your lures allow because the fish seem to stand a bit away from the shore a lot. The fish finder will also give you clues which depth range might be successful at all and where the fish are more concentrated. But beware that fish standing shallow will often not show up on the fish finder ( because they don't come into cone of sound waves) and you should give shallow running lures a try even without any signals on your fish finder. Don't just concentrate on signals of big fish, schools of bait fish are at least as important.
Deeper Down To The Fish
If you've been trolling for a while you'll develop two wishes:
getting the lures deeper down and spreading them farther out to cover more water
in a single pass.
For additional depth you could use downrigger or a diver. The downrigger is a
heavy chunk of lead which is let down on a steel cable. on the lead or the cable
there is clip into which you can fix you're line (you could also use thin rubber
bands or even pieces of light line). So now the line runs from our rod more or
less straight down to the big lead and from there horizontally to the lure. If a
fish bites the connection of the fishing line to the downrigger should break and
you can fight the fish unimpaired by heavy lead weights.
If you want to cover a broader area when trolling you will need a planer board which makes the lure run sideways of the boat. These boards swim on the water and are attached to the line in such a way that they veer out when you pull them, being able to run up to 50 Meter sideways of the boat. There are two basic ways of using them: either you attach them straight to you fishing line, that's usually called an inline planer board or they are attached to a mast with a line of there own, the fishing line is then attached with a clip similar as to a down rigger. Traditional models in the alpine region have so called "Zügel", attached directly to the planer line without using a rod at all. For the inline models you will also need a heavier rod because they work with water pressure just like the divers. Apart from the advantage of covering a larger area we've now also got better chances to catch boat shy fish and can go very close to the shore with a shallow diving lure.