Build heaps of T1 fighters, they are cheap and if you are T3 then they get built quite fast
Build 50-200 of them and make sure that you have good radar coverage and/or some scouts, T1 if you don't want to stuff up your economy.
Or you can just build another T3 power and 3 T3 fabricators quickly and use the extra resources to build T3 ASF's and scouts.
Or, this will help you in the longer run, build some SCU's because they produce their own resources and build the quickest out of anything. You then use them to build more and more power and mass fabricators. You can then mass produce aircraft and use the SCU's to help build them.
These will all work, just choose the one that works the best for you.
Hope this works