A few things that you need to keep in mind.
An indulgence is simply a modern application or method of preforming ancient penances. In the early Church penances were very severe by our standards. Today they are commuted to less severe actions, including those imposed by the priest when we are in the confessional. If you normally rode a horse ten miles a day, and the penance imposed on you was to walk and not ride your horse for six months, or two years, that was much harsher than what we do today.
To gain an indulgence, you have to make an intention to do so, they don’t come automatically. So if you make the inention (even once a year that let’s say, “All rosaries that I pray this year be means of gaining an indulgence) you will gain them. If you don’t make the intention, you still benefit spiritually but don’t gain the indulgence.
Those Indulgences you do gain, are only gained when you are not in a state of mortal sin. So make an intention once a year to gain all the indulgences that are availible to you by any prayers or charitable/holy acts, go to confession and receive communion on a regular basis. You will be fulfilling your obligations to God to live a holy life, and grow spiriutally, and as a bonus, you will gain many indulgences that you don’t even know exist.