Some evil people would tell you, that it is important to do missions for a corporation, whose loyality points (aka LP) gives you most ISK per point (good rate is 1,5 isk per point, you can get 2 or even more, but not constatnly, market changes) but I think it is more important to find place you wnat to live in. My eyes bleeded badly after missioning in Langissi. Cause of red minmatar nabula. So you take your time, fly around, find place you like, where you can feel yourself home…
After that you use agent finder http://ea.omg-cdn.net/ and dotlan map http://evemaps.dotlan.net/npc to find out, who offer level 4 security missions there. Use “buy prices” button on https://www.fuzzwork.co.uk/lpstore/ (with The Forge selected) to find out, who offer better LP / isk ratio. Make your choice and get back to Dotlan - now you have to plan your standings grind for that corportation. Buy yourself Gnosis and learn how to fit / fly it untill you get skills.
Google up eve-survival web site - it will give you infromation about what damagge type to apply and what are the triggers in missions. If you want , you can read up Blitz and Burner Guide v1.2.3, many mission runners try to blitz missions, but for me it is a boring repetitive job, thogh very ISK effective. I like unpredicatbility of loot, different views in different missions, so I do not limit myself to 5-6 missions but do any I like. Game, not the job, remember? 