Jester mentioned there are no blogs by a market guy.
Jester calls himself an industry guy and not a market guy, so he does make a distinction by the two. Because while pure market blogs are very rare indeed there are enough blogs that cover industry. Most blogs cover various aspects of pvp though.
Ardent Defender explains again why there aren't that many market blogs and one of them is because market traders like to protect their own markets. So instead of giving a step by step guide of how they make their money most only give out the general strategies and leave it to the reader to find their own items and stations where to trade.
Of course specifics are not always that interesting. At the moment I live in nullsec fulltime, so only blues have docking rights and the CFC has rules against buying up someone's stock and relisting it for a higher price in the same or another blue station. It does happen though.
With Jita over 30 jumps away people buy locally and and as few stations as possible. Since stations are also less well stocked this means profit margins can sometimes be quite high.
On the other hand I tend to put modules on market with about 10-15% mark-up most often making me amongst the cheapest within a dozen jumps.
A few weeks ago I started my first venture. I took a look what modules I myself needed and expected others to need. Then I looked for modules that were either overpriced or not available locally.
In the end I choose the following items, based more on personal preference as the biggest profit margins or turnaround:
25 1600mm Reinforced Rolled Tungsten Plates
50 Adaptive Nano Plating II
200 Heavy Assault Missile Launcher II
60 Focused Medium Pulse Lasers II
40 Heat Sink II
125 Warrior II
I moved or had them moved to Branch and put them on market. The original stock is long gone. Some other people put the same modules on market later. In some I lowered my margin to be cheapest again and in other cases I switched to other modules.
So by now I have removed Adaptive Nano Plating II from my list and added some others.
Cap Recharger II
Drone Damage Amplifier II
Magnetic Field Stabilizer II
In between I put some shield hardeners on the market but those don't give enough profit right now to restock.
It's only small scale so far, or at least small scale for most I guess. For me it ties up the majority of my liquid isk leaving me with less as a billion. So far I invested about 2.7 billion in T2 modules. Sold about 2.3 billion in modules and about 800 million still on the market to sell.