The process of purchasing and upgrading properties is one that all characters should consider wisely, as they tend to have high costs, long build times, and often define the player's consistent income.
There are two general stages of property management, loosely divided by the purchase of the player's first Fortress.
Pre-Fortress Strategy Edit
In the early game, you'll need to focus on attaining the highest possible hourly income as quickly as possible. In general, this strategy makes the purchase of other upgrade properties, gear, vehicles, and healing much easier throughout the rest of the game. It does delay the onset of the benefits granted by upgrade properties, however.
A player taking this approach is advised to upgrade each type of property to the maximum level prior to purchasing the next property. Take breaks to purchase only Safehouse upgrades, trying to keep your safehouse capacity roughly 10- to 12-times your hourly income. Each time you upgrade the safehouse, it will also slightly increase your hourly income rate.
Continue purchasing only income properties until you own all possible Bars, Restaurants, Condos, and Night Clubs. This will bring your hourly income to $22,250/hr (including a level 4 safehouse). At this point, you're best served building Real Estate Agencies and Construction Companies until they're each maxed-out at 10 each. Most players alternate between the two, but you can build them in any order you want.
Once you've got these built, go back to buying income properties. Do this until you have 10 Mansions. This will likely require a safehouse upgrade to facilitate a higher limit.
Now that you have a steady income from these properties, it's time to upgrade your Hospital and Arms Factory to maximum levels. This will reduce the ever-increasing money sink that healing (required for Bosses and PvP) and equipment (required for Jobs) become as you advance in level. After you've got those max'ed, start working on Boxing Gyms and Personal Armories, which will increase increase your Attack and Defense by 50 each when dueling and by significantly more when warring, as you'll add the bonuses to each lieutenant you own.
After you've got all these properties, it's time to update your safehouse to level 6 (you may have already done this), and then buy your Fortress.
Alternative Strategy Edit
As an alternative, you may want to focus on getting the most statistical bonuses from your properties as fast as possible. If this is the case, use the above strategy, but seed in hospitals and arms factories sooner, alternating between one of each available upgrade property and income properties. This will slow down your rate of income but will allow you to more quickly save money that would otherwise go to healing and weapons. After you've got these built up, work on real estate agencies and construction companies. Once you have the largest possible discount on properties and reduction of build times, crank out boxing gyms and personal armories.
This strategy is much less regimented than the primary strategy, and isn't as efficient in terms of getting a fortress sooner, but it does help many players feel like they're actually benefiting from their properties along the way.
Post-Fortress Strategy Edit
Each time you build or upgrade your fortress, you'll increase the building limit of all income properties (except bars) as well as all post-fortress upgrades. It is recommended to buy an additional upgrade for each income property to keep them maxed out as soon as possible after building a fortress. If you have not yet purchased any Casinos or Carribean Islands, you may also want to do so now to help you afford the increasingly expensive upgrades to your fortress and other post-fortress upgrades.
The first post-fortress upgrade you should get each time you upgrade your fortress is the Dojo, which requires no prerequisites and has nothing else dependent on its being built.
Now it's time to set your first post-fortress goal. In almost every case, you must build a series of upgrades before getting to the ones that increase player attack, defense, energy, and stamina. Pick the stat you want to boost first based on your character build and build each property required to reach it without getting distracted along the way with parallel buildings.
After reaching your first goal, fill in all the gaps already opened by previous purchases, then move on to your next target. Along the way, you'll unlock the ability to upgrade your fortress. In general, it's best to get all non-income, non-safehouse upgrades before increasing your property limit.
By this point, it's generally not worth it to build the Stock Market Exchange simply because its cost is one iteration higher than similarly tiered properties and its benefit is unlikely to be needed or even noticed once added. Thus, if you want to skip a property after getting your fortress, this is the one you are least likely to regret. Note that you'll need to have 5 SMEs before you can upgrade to a 6th-level fortress, however.
If you don't have specific goals in mind in terms of post-fortress upgrades, it is recommended to work always toward the next fortress upgrade first. This means building the following (property level indicated in parentheses) as soon as possible each time you upgrade your fortress: