This is is very, very, very, very, very important. The higher your construction speed the faster you build your buildings. The 1st city there is nothing you can do but have a slow construction speeds. After the 1st city you can use a cottage build method. I am going under the premise that you have followed earlier advice and installed the city planner. It also uses the presumption that you will be building quarry and woodcutter huts along with the cottages to ensure you have resources.
The method goes like this:
Level 1 Town Hall (TH): 5 cottages built to level 2; Build TH to level 2.
Level 2 TH: 5 new cottages built to level 2, increase 1st 5 cottages to level 3; Increase TH to level 3.
Level 3 TH: 5 new cottages, All cottages to level 3; Increase TH to level 4.
Level 4 TH: 5 new cottages, All to level 3; Increase TH to level 5.
Level 5 TH: 5 new cottages, All to level 4; Increase TH to level 6.
Level 6 TH: 5 new cottages, make all to level 7; by this point you have 30 cottages! Build TH to level 7.
Level 7 TH: 5 new cottages to level 4, increase the others to level 8; Build TH to level 8.
Level 8 TH: 5 new cottages to level 4, build TH to level 9.
Level 9 TH: 5 new cottages to level 4, increase level 8 cottages to level 10; build level 10 TH.
Level 10 TH: no new cottages, increase 15 cottages to level 6.
Build all other buildings to level 10 under the speed of 4000%+. Once your buildings are all to level 10, begin destroying cottages, to replace them with resource buildings. You want to only destroy 2 cottages at a time to build just as quick the replacement buildings.
You modify this a little for castle builds. you change the number of cottages to 6 instead of 5, and build your recruitment buildings 1st since they take longer than barracks.
This should help speed up your constructions; once perfected you can build a castle in 36 hours! I have made several this way in that time frame.