Skill Discussions

Skills that add order (both buy and sell) slots:
Trade
Retail
Wholesale
Tycoon

Trade + Retail level 5 plus a level or three of wholesale should be plenty but you be the judge of that. A lot depends on how many different things you need to sell/buy at the same time. IIRC The Trade skill alone will give you 20 slots at level five. Note that you're better off training Trade IV + Retail I than Trade V.

Skills that lower market costs:
Accounting
Broker Relations

In addition to the skills also your standings towards the station owner affect the broker fees. There was this nice graph on the net that explained the whole thing, see if you can find that.
EDIT: found the graph, http://go-dl1.eve-files.com/media/corp/Thoraemond/eve-market-order-broker-fees-20110417.png

Other skills:
Margin Trading might be useful if you don't have a lot of ISK at your disposal. The only remote skills useful might be the skill that allows changing order prices remotely, Daytrading.

social + connections raise your standings with npc corps.
If u train them both to 4 (not too much time) you will get nice boost.

I disagree with Sable somewhat.

Accounting
Broker Relations
These are the two most important trade skills for an industrialist. You will be buying and selling large quantities of goods, and fractional percents on taxes and broker fees really add up. These are the first two skills in the group to get to 5.

Margin Trading
This is very important for leveraging your wealth. It allows you to start setting up buy orders for your raw materials before you have fully sold your previous stock. This keeps your factories going and the profits coming in. However, it can be dangerous if you are not careful. You can have some of your orders cancelled and the fees forfeit. Level 3 is probably good for a while.

Marketing
Procurement
Day Trading
These three are also vital. You will be spending a great deal of time in your home system starting jobs, hauling, and doing whatever else you do. But your buy and sell orders will be in a market hub elsewhere. So you will need to remotely set buy and sell orders and modify them from across the region. Train these to level 3 if your home system is less than 10 jumps to the market hub. Train them to 4 if you spend much time more than 10 jumps from your hub. There is probably no need to train them to 5.

Then the list of skills to give you more market orders:
Trade
-Retail
--Wholesale
---Tycoon
Only train these skills when you notice that you are running low on market orders. Trade 4 is 17 market orders, which is really enough to get you started on a couple items in one market hub. Get a couple levels of Retail when you expand to more items or multiple markets. You will be a very large operation before you need a level of Wholesale. If you are getting Tycoon, you are probably making more money station trading than you are with any industrial venture.

Connections doesn't raise standing, only effective standing. But that does lower sales tax. It's important to note that you need a positive standing, ven just 0.01, in order for Connections to towke

Social does nothing unless you're flying missions to earn standing.

Edit: Wait, I'm not sure if Connections modifies sales tax or not. I just assumed it did. I do know it affects ore refining tax in stations, the "we take" part.