The missions you encounter are randomly selected. Though, you will see that the ratio of the different types of missions is dependant on what division your agent works in. You can see a breakdown of this on the website here. Also, the missions you receive are usually racial related, so the Ammar have more missions against the Minmatar and Blood-Raiders while the Caldari will offer similar missions against the Gallente and Guristas.
I would also check EVEinfo You'll get allot of usefull information about mission there as how many ships are there and what damage type you should tank
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The missions you encounter are randomly selected. Though, you will see that the ratio of the different types of missions is dependant on what division your agent works in. You can see a breakdown of this on the website here. Also, the missions you receive are usually racial related, so the Ammar have more missions against the Minmatar and Blood-Raiders while the Caldari will offer similar missions against the Gallente and Guristas.