Hi

Specific tactics depends on the business, but usually you should try to go for the niches for which your product is much better. There, are probably much more incline to switch (they usually feel neglected by the incumbent player)

The other thing that works well is optimizing what you do today in order to be more effective at acquiring customers and converting them - bigger efficiency can compensate to some extent for lower budget / resources.

The last group of actions is finding a way around the current information distribution system so you can bent the rules in your favour (this really depends on the nature of your business, segments targeted and the way the information flows). The usuall suspects are: getting refferal system for happy customers you can spread the world around (i.e Dropbox), affiliate programs, getting influential evangelist (i.e. Canva and Guy Kawasaki) or tones of small but with some coverage bloggers / local opinion leaders (i.e. Buffer)

Hope it helps

Best regards
Asen