The link to the invention guide that I posted is pretty good but in my opinion but Iíll try and distil it a little bit below. Iím going to split it into 3 sections skills, materials, and blueprints.
From a skills point of view there are 2 science skills that relate to every blueprint that you might wish to perform invention on. If you look at what the skill requirements are on the invention tab of the blueprint these will be listed.
The impact of these skills is twofold, firstly the level of the skill has an impact on how successful an invention job will be, and what level R&D agents you can use in order to get datacores (more on this in materials). For missiles the 2 skills are Rocket Science and Electronic Engineering.
I would train both the skills to level 4 personally and then have a think about whether you want to go to level 5. Training to level 4 will give you access to level 4 R&D agents (as long as you have the standing) and training to level 5 is generally a long haul.
Each blueprint also has a related race (one of the four empire races) and you will also the racial encryption method skill relevant to that race. The only impact of the level of this is on your invention chance. Nearly all, if not all, missiles are Caldari so if you want to specialise here I would train this to level 5.
The only other thing that impacts on your invention chance are decryptors and a corresponding tech 1 item, Iíll come onto those in materials, ignoring them for now your invention chance is calculated as
Invention Chance = Base chance on blueprint * (1 + (Racial encryption skill level * 0.01)) * (1 + ((level of 1st science skill + level of 2nd science skill)*0.02))
So if you have science skills both to level 4, and the racial skill to level 5 as above, then for ammo, which has a base chance of 40%, the chance of successful invention is
Invention Chance = 0.4 * (1 + (5 * 0.01)) * (1 + ((4 + 4) * 0.02)) =0.4 * 1.05 * 1.16 = 0.4872 = 48.72%
Generally think of this as a one in two chance so if you place 10 invention jobs expect roughly 5 successes.
Most materials are consumed in the invention process and the cost of these materials is something that you will need to consider when calculating your profit on tech 2 items. Remember if your invention chance is 50% you need to double your material requirements when calculating the cost of an invented T2 BPC.
The first thing you will need is a data interface; there are 3 types of data interface for each race. On the blueprint you want to invent under the invention tab it will tell you which one you need. This is the only component NOT to be consumed in the invention process and so can be left out of the cost of your T2 BPC.
You also need datacores that are related to each of the required science skills, so Rocket Science and Electronic Engineering for missiles, the blueprint will tell you how many and which ones you need. Other than buying them from the market these are obtained from R&D agents. Not all R&D agents can provide every datacore so you need to find an agent that will give you the datacores you need and then gain the standing and the skills to use that agent. The higher the agent level the faster they produce datacores. Alternatively they can be bought on the market.
If you need a separate guide to R&D agents let me know and Iíll put something together.
There are also 2 optional components that impact the chance of a successful invention, these are a corresponding tech 1 item of the blueprint you want to perform invention on and decryptors.
For tech 1 items the metal level of the item increases your level of your science skills in the formula above. So if you use a meta level 3 item then your science skills are effectively 12 and 12 (4*3) and as a result your final invention chance is 62.16%
Whether or not this is worth it depends on the cost of the meta level of the item and has to be judged on a case by case basis. Generally I donít bother but itís up to the individual.
Decryptors are more complicated. They have an impact on the number of runs, the ME level and the PL level of the final T2 blueprint as well as the probability of successful invention. Some decryptors actually decrease the chance of invention but you will get a better quality T2 BPC. Generally these are so expensive that you shouldnít bother but if you want to get into inventing T2 ships it could be worth looking into.
Most blueprints only have one T2 blueprint that you can gain from invention, however some, including missiles have two options. The type of T2 blueprint that you want to invent is selected as part of the invention process when you place the invention job. In the case of missiles you have the option of a high damage or a high range variant.
You can only invent an item from a blueprint copy. So the first step is to copy the BPO that you want to create a T2 version of. The ME and PL level of the BPO have no impact at all on the invented T2 BPC so there is no point researching your BPO if all you intend to do is invent from it.
The only thing that has an impact on the resulting T2 BPC is the number of runs your T1 BPC had.
If you want to calculate how many runs your T2 BPC will have then you need to the formula below.
T2 BPC Runs = rounddown((T1 BPC runs / max T1 BPC runs) * (T2 max BPC runs / 10))
You can never have more runs than the max runs on the T2 BPC you are looking for and you will always get a T2 BPC with at least one run. As a general rule I always make sure my T1 BPC has the maximum number of runs and then every successful invention will give you a T2 BPC with one tenth itís maximum runs.
As mentioned above, the number of runs on your T2 BPC can also be affected by the use of a decryptor.
In summary you need the following in order to place an invention job.
Relevant science skills (to level 4/5 ideally)
R&D agents researching the relevant datacores
Max Run T1 BPCís