First, it has been my observation that the system core is usually fairly remote from where you start. So, while exploring the board I try to cross it in both X and Y, then explore the edges, then backfill.
Second, know your utilities and how they work. Generally, to use a utility you click it then you click on a defensive node. There are some nuances worth mentioning.
- Repair Subsystem: unlike other utilities, this one does not target a defensive node. It just adds to your
hitpointsvirus coherence regardless of what you click. That is, it functions even when you are just clicking on unexplored nodes. Since there is never any downside to having a large virus coherence, you should always use each Repair Subsystem immediately.
- Polymorphic Shield: this utility protects you from any two attacks, from the same node, or different nodes. Thus, it is often the case that you can use it on two different defensive nodes. For example, 50/40 firewalls are fairly common in nullsec sites. If you have virus strength 30, as I do, these can be killed in two hits. But two hits means they get one hit back: 40 damage. Ouch! Say that you've uncovered two of them. If you activate a Polymorphic Shield, then click one, and then the other, each node will be knocked down to 20/40 without hurting you. You can then click each one again; this time you destroy them and because it is the last hit, you don't take any damage.
- Secondary Vector: this utility does 60 points of damage to a defensive node, over 3 turns. You do not have to attack the defensive node yourself once you've activated the utility and selected its target. And it is often best not to, limiting your own damage. As an example: you run across a hated Virus Suppressor (60/15). It halves your virus strength; thus, with 30 strength initially you've got 15, and it will take 4 hits to kill the Suppressor, during which time it will do 45 damage to you. Ouch! However, you can kill it without taking any damage using a Secondary Vector so long as you have some unexplored nodes left: activate the vector, click on the Suppressor, then go click some other nodes for 2 turns. The Suppressor takes 60 damage and poof it is gone; you don't take any.
Third: know the enemy. Here are the list of the defensive nodes, in order of their nastiness, as well as strategies for dealing with them.
- Virus Suppressor: these things are the worst. The ones I have found are always 60/15. 60 strength does not seem that bad until you realize that your own virus strength is halved when fighting it, so 60 is more like 120. You'll want to eliminate them ASAP. If you have a utility of any kind, use it. Secondary Vectors are preferable. Because Virus Suppressors do so much damage, it is worthwhile trying to find a utility to help kill them.
- Restoration Node: a close second in nastiness. The only good thing about them is that their damage is moderate. The ones I have found are always 80/10, so with 30 virus strength they do 20 damage. Because their effect is nasty, I usually kill them ASAP. Because their damage is moderate, I usually do not use a utility on them.
- Anti-Virus, Firewall: not a huge threat. You should never attack one of these if it will damage you, until you are completely blocked everywhere else.