One trick that led me to get more guild marks is to get 2-3 leves per city and max it out to 8. Then when I get to a city that offers a leve with marks, I can exchange that leve with my previous leves from another city, potentially doubling the amount. I once got 4k mark on my CON and 3.8k on my THM, when a faction leve offered 2k leve and I got to exchange 4 leves for each of them. after the exchange, the marks are twice the amount it originally offered. So don't just take the level right away, if you have leves from the previous cycle, exchange them. It is more worth when your old leves are from a different faction or city.
Mikayla Soulfire (XIV), Ul'dah, Istory Lodestone Profile
Mikael (XI) Bastok, CaithSith
Thus is our agreement written, thus is treaty made. Thought is the arrow of time; Memory never fades. What was asked is given; The price is paid.