In 1.0 and later, it's largely through doubling upgrades.
The base rate is 0.5 CpS, or 0.8 after you buy Forwards from grandma.
This increases by 0.02 for each grandma after buying One mind, an additional 0.02 for each grandma after buying Communal brainsweep, and 0.05 for each portal after buying Elder Pact.
The rest of the grandma upgrades make grandmas 2^18 = 262,144 times as efficient.
- Six upgrades that double the rate are unlocked after having hired specific numbers of grandmas: 1, 5, 10, 50, 100, and 200.
- The nine grandma costumes are unlocked for having at least 15 of each building (Farm through Prism). These are also doubling upgrades.
- Buying seven grandma costumes unlocks Bingo center (quadruple); waiting after that unlocks Ritual rolling pins (double).
- During Christmas, the "festive hat" upgrade chain will eventually unlock Naughty list (double).
Once you enter the Grandmapocalypse by buying One mind, part of the grandmas' production actually becomes quadratic (O(n^2)) because the base rate for each grandma includes something multiplied by the number of grandmas, and that in turn is multiplied by the number of grandmas. With more than 40 grandmas, the majority of your production is from quadratic effects.
As with every other source of cookie production, this is multiplied by your cookie production multiplier (mostly flavored cookies and heavenly chips), egg multiplier (Easter-related), covenant multiplier (95% if in effect), frenzy multiplier (usually 100%, occasionally 700%, 50%, or 66600%), and wrinkler multiplier (100% to 600%).
Sources: "Grandma", "Upgrade", and "CpS" pages on Cookie Clicker Wiki
It depends on your motivations for playing but the newest target is 200, and beyond that, there are no imperative reasons to purchase any more. If your only goal is to have everything currently available, then you can stop once you have all achievements, all upgrades, 240 cursors and 200 of everything else, got all the seasonal purchases and clicks, 7777 lucky cookie clicks, and have reset 12.5 quintillion cookies away as there is currently nothing beyond that.
You may optionally want to try to optimize CPS gains by balancing out cost/cps for building purchases in order to make more efficient progress later, but that is entirely optional and may not prove to be worth your effort depending upon what is to be added. Because the cost/cps is better on some of the lesser buildings when compared in equivalent quantities of other buildings, your most efficient CPS purchases will be from some of these cheaper buildings. Essentially you would calculate buildingCost/(cps/building)=cpsCost for your most profitable building and then purchase enough of every other building to get the cpsCost for each building to be approximately the same value as was calculated for the most profitable (because they will have the worst cost/value if you don't try to balance the cpsCost). It should be noted that the cost/value relationships change as you purchase upgrades. Having a spreadsheet helps.
Best Answer
The main way to increase the frequency of golden cookies is by getting achievements related to collecting them. Specifically after collecting 7, 27 and 77 of them. Each of the upgrades make cookies appear "twice as often" meaning the time between them is cut in half. There are other way to increase frequency of them by smaller increments listed in the wiki link.