The answer to your question is extremely complex but I'll try and give you some pointers.

The most important thing I would say is to set yourself targets. Decide how much money you want to make and then keep that in mind when setting up any industry.

Say you want to make enough to buy a PLEX a month which is about 350 mil. If you can run 5 production lines each one needs to be making 70 mil a month or (aprox.) 2.5 mil ISK a day. So if you can produce 125 lasers from a 1 day production run, you target needs to 20,000 ISK profit per laser. If you are about to place 100 sales order on the market, then each order needs to be making 3.5 mil per month so you need to be selling 175 of those laser per month. There are skills that increase the number of production lines you run and reduce the manufacturing time (Production Efficiency research on blueprints also brings this down). These can be used to lower your targets without affecting your profit.

You profit is your profit margin (sales price - cost to produce) x number of sales, so there are 3 ways to increase your profit. Reduce costs, increase sales price or increase number sold so keep an eye on all 3 of those factors.

Costs can be reduced through skills like Product Efficiency (lvl V is a must!), Accountancy & Broker Relations. Taxes are reduced if you have a good Rep where you sell. Researching blueprints will reduce the amount of materials required. Be aware that research has a diminishing return, the first lvl save 5%, the second 1.67%, the third 0.83% and so on and there is also a maximum efficiency beyond which no further saving is made. Buying your building materials at lower prices also helps but this usually means buy-orders placed over large areas which leads to lots of travelling around collecting stuff. You may be able to find a corp. to supply you but I have had no success in doing this so I won't comment further.

Sales price can be increased by finding the right area to sell ie where demand is higher than supply. Also some markets can be manipulated by buying up all the available items and then selling at a higher price (I'm not very experienced at this so I won't say more).

Number of sales is again down to the right location. Sometimes a price reduction will increase sales, if your prices are too high but not often. The best way to increase sales is move to a market hub but prices will be more competitive (i.e. lower) so this option is a trade off.

There are two ways to get stuff to sell, you either build it or get loot (or other peoples loot through buy orders). So keep an eye on the buy orders for anything you are interested in selling. If it'll cost you 50,000 to make but only 5,000 to buy through orders then if you make it you are competing with people with much lower over heads. They can sell for 45,000 and still be making a good profit when you are making a loss. You have the advantage of much better supply as you can build what you want, when you need it and this can be enough of an advantage to make the market profitable for you.

Too be honest, it is something that you just have to have a go at and see if you can make it work. It will involve a fair amount of effort especially at start up but there is definitely money to be made. There is a lot of trial and error involved but don't worry about this. Try it, learn from it and if it does not work then ditch it and move on.

A couple of final thoughts: Remember to take all costs in to account this includes minerals that you mine. They may not have cost you anything to get but you could just sell them and make money without effort.

Don't massively undercut other people sales prices. You will not have some secret way of producing items cheaply and so if you can afford to sell at a lower price then so can they. All you do is reduce the overall profit margin on that item. The exception to this is when prices are just too high to be competitive and nothing is selling due to it. When you master the markets and are able to manipulate them, then ignore this advise (in fact tell me how you do it!).

Ships are a tough market to get in to. Ammo and drones get used up so there is higher demand for these.

Good Luck

Additional

One other point worth mentioning is that markets ebb and flow. You will find some products where there is good money to be made and so you start trading but others will spot this and do the same. This will bring in high competition and the price will fall and the profit will be gone. But give it sometime (can be a few months) and eventually everyone will lose interest in this market and stop trading and the price will then rise and be worth trading again.